Pollutant Load Reductions for Total Maximum Daily Loads for Highways (2013)

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3 OBJECTIVE This synthesis was designed to acquire information on the types of best management practices (BMPs) currently being implemented by state departments of transportation (DOTs) to meet total maximum daily load (TMDL) water quality goals for stormwater runoff. It seeks to establish the existing “state of knowledge” of DOTs as it relates to TMDL implementa- tion strategies to facilitate information sharing and technol- ogy transfer for the mutual benefit of all DOTs. The results of DOT interviews and highlights from key research studies are summarized; challenges and successes that DOTs have experienced have been identified; and this information has been organized, evaluated, and documented into usable cat- egories for the benefit of DOT officials responsible for man- aging TMDL programs. This synthesis will ultimately pro- vide a summary of key information on effective and practical BMPs for highway TMDL implementation. This study is not intended to cover all literature sources, but rather high- light the most important information from a select group of sources specifically related to highways, TMDLs, BMP performance, and BMP cost. Throughout the text there are references to sources where the interested reader may obtain more detailed information. TOTAL MAXIMUM DAILY LOADS AND THE REGULATORY FRAMEWORK FOR STORMWATER MANAGEMENT TMDLs are a requirement under §303(d) of the Federal Water Pollution Control Act (Clean Water Act or CWA) of 1972. Under that law, states are required to develop lists of water body segments impaired by a pollutant and needing a TMDL. A TMDL is a technical calculation of the maximum load of a pollutant a water body can receive and still meet water qual- ity standards. A TMDL addresses the sum of all point source loads (waste load allocation) and loads associated with non- point sources (load allocation) (EPA 2009). TMDL WLA LA MOS= + + Where: WLA = waste load allocation (amount of pollutant from existing point sources; e.g., sewage treatment plant, industrial facility, stormwater); LA = load allocation (amount of pollutant from existing nonpoint sources and natural background; e.g., farm runoff and atmospheric mercury); and MOS = margin of safety (part of TMDL allocated to uncertainty in analysis). TMDLs are generally developed by states or the EPA. Some have also been developed by third parties in conjunction with states. The development process is based on the load- ing capacity of the water body (i.e., the maximum amount of loading that a water body can assimilate and still meet water quality standards) and the pollutant reductions needed to meet the loading capacity. In this way, TMDLs are an important link between watershed pollution control actions and the attainment of water quality standards (EPA 2012a, b). TMDLs are generally implemented at the watershed scale through WLAs incorporated into DOT’s National Pollutant Discharge Elimination System (NPDES) permits for storm- water discharges from municipal separate storm sewer systems (MS4s) and construction permits. From a DOT perspec- tive, TMDLs are an emerging issue and some DOTs confront increasing economic and technical challenges associated with TMDL implementation. DOTs face unique challenges because roads are linear entities that often cross many water- sheds and therefore the DOT may be named a stakeholder in multiple TMDLs. Effectively addressing TMDLs requires watershed modeling tools to calculate baseline pollutant loads within and adjacent to the DOT right-of-way (ROW) and to predict the pollutant load reductions associated with BMP implementation. In addition to TMDLs, many regulatory requirements affect DOT stormwater management activities. Histori- cally, DOTs have been effective at addressing drainage and hydraulic issues related to the maintenance of the transpor- tation infrastructure (FHWA 1979). This includes design standards that (1) ensure that stormwater runoff is conveyed away from the road surface quickly and efficiently, and (2) minimize maintenance needs by ensuring self-cleansing velocities in pipes and ditches while also avoiding exces- sive velocities that would require repeated repair of grass- lined channels. In some states (e.g., Virginia), the increases in peak flow rates resulting from these policies have resulted in state- or watershed-driven requirements to manage storm- water discharges to minimize downstream channel erosion and flooding. chapter one INTRODUCTION

4 Some states such as Maryland and Virginia have also estab- lished statewide regulations that require DOTs to implement post-construction stormwater quality and quantity BMPs on new and widening road projects. These requirements have generally been the result of either specific watershed initia- tives [e.g., the Chesapeake Bay and the Neuse River (North Carolina)] or other resource or habitat protection goals (e.g., salmon). Finally, the EPA’s development of NPDES MS4 permits has regulated the quality of stormwater discharges from the DOT drainage system. These MS4 permits are generally updated every 5 years to include any additional require- ments of local TMDLs. However, in some cases permits may be updated more frequently (e.g., Washington State, where they are updated at least every 18 months) or less fre- quently (in some states permits are 10 or more years old). In the absence of a TMDL pollutant of concern, the NPDES MS4 permit requires general post-construction stormwater treatment for runoff generated by the newly constructed ROW, as well as a program for identifying and eliminating illicit (nonstormwater) discharges to the ROW. Therefore, many DOTs are implementing both programmatic (e.g., illicit discharge detection and elimination) and technical water quality improvement projects within all or limited areas of their states. The development of TMDLs adds specificity to the DOT’s MS4 permits in terms of specific pollutants and/or specific compliance requirements. In addition, incorporating the requirements of the TMDL into the MS4 permit provides an additional CWA enforcement provision to the TMDL, which is a relatively new element of the MS4 permits. PROBLEM STATEMENT Because TMDL implementation is generally new for DOTs, BMP strategies tend to rely on traditional end-of-pipe treat- ment approaches. However, there are several drawbacks to these types of BMPs, including (1) there are possible public safety issues, (2) they are expensive to design and construct, (3) they have a large construction footprint in a ROW that is often needed for other purposes, (4) they require intensive maintenance to ensure continued performance, and (5) they may not be effective at removing certain pollutants. Although some DOTs have added a new class of higher-performing and smaller footprint BMPs to their stormwater quality toolboxes (e.g., infiltration, bioretention, and filter strips), as well as some innovative BMPs and even low impact development/ green infrastructure practices, there is still a need for infor- mation on what practices are specifically effective for TMDL implementation for highways. Further, there appears to be little awareness of the types of design standards, operation and maintenance requirements, monitoring and performance objectives (especially types of TMDL pollutants treated), and BMP costs that are needed to meet TMDL water quality goals beyond the normal compliance framework to meet MS4 permit requirements. TMDLs require many DOTs to face unprecedented challenges to achieve target reduction goals. Further, TMDLs are generally increasing in number across the country and in some states potentially hundreds of additional TMDLs will be developed in which the DOT may be named a stakeholder. To help fill in these information gaps, this synthesis will summarize current effective and practical methods for DOTs to meet TMDL requirements for highways, particularly given the land and budget constraints that DOTs often face. Although there exist many studies on BMP performance, and some on BMP costs, there is limited information on the types of BMPs that are applicable to the linear highway environment and even fewer reports that address TMDL implementation issues. Because this study will synthesize all of these topics, it focused on using the criteria of highways, TMDLs, BMP performance, and BMP cost to refine our approach and meet the goals of this synthesis. Our research is not intended to be comprehen- sive, but rather present highlights from key sources that meet the previous criteria and would be most relevant to DOT man- agers. Information will also be obtained on potential opportu- nities to form off-site (i.e., outside the ROW) partnerships (or any barriers to such partnerships) to reduce external inputs of pollutants onto the DOT’s stormwater system on a watershed- wide basis. This type of approach may potentially be more cost-effective (and potentially more credit-worthy) than BMPs implemented strictly within the DOT ROW where space is limited, especially in ultra-urban areas. Finally, this study will develop a matrix/toolbox of some of the more common struc- tural and nonstructural BMPs employed by DOTs for TMDL implementation within the unique highway environment. We hope this study will provide new and practical information for the benefit of DOT highway practitioners who are developing their TMDL programs. REPORT ORGANIZATION This synthesis report is divided into five chapters. The first chapter presents introductory background material. The second chapter includes the basic study approach, including methods for conducting the literature review and the state DOT interviews. The third chapter includes the major find- ings of the literature review and interviews and synthesizes them into usable categories (e.g., BMP design, maintenance, and cost), and provides several detailed examples of indi- vidual state DOT implementation plans. Chapter four pre- sents a BMP matrix/toolbox that provides performance and life-cycle cost data for structural BMPs used by DOTs in the highway environment, as well as performance data for nonstructural BMPs. Finally, chapter five draws conclusions based on the accumulated information and identifies areas for further research.