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Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff (2019)

Chapter: Chapter 8 - Effectiveness of Innovative Solutions

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Suggested Citation:"Chapter 8 - Effectiveness of Innovative Solutions." National Academies of Sciences, Engineering, and Medicine. 2019. Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff. Washington, DC: The National Academies Press. doi: 10.17226/25473.
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Suggested Citation:"Chapter 8 - Effectiveness of Innovative Solutions." National Academies of Sciences, Engineering, and Medicine. 2019. Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff. Washington, DC: The National Academies Press. doi: 10.17226/25473.
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Suggested Citation:"Chapter 8 - Effectiveness of Innovative Solutions." National Academies of Sciences, Engineering, and Medicine. 2019. Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff. Washington, DC: The National Academies Press. doi: 10.17226/25473.
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Suggested Citation:"Chapter 8 - Effectiveness of Innovative Solutions." National Academies of Sciences, Engineering, and Medicine. 2019. Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff. Washington, DC: The National Academies Press. doi: 10.17226/25473.
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Suggested Citation:"Chapter 8 - Effectiveness of Innovative Solutions." National Academies of Sciences, Engineering, and Medicine. 2019. Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff. Washington, DC: The National Academies Press. doi: 10.17226/25473.
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Suggested Citation:"Chapter 8 - Effectiveness of Innovative Solutions." National Academies of Sciences, Engineering, and Medicine. 2019. Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff. Washington, DC: The National Academies Press. doi: 10.17226/25473.
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Suggested Citation:"Chapter 8 - Effectiveness of Innovative Solutions." National Academies of Sciences, Engineering, and Medicine. 2019. Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff. Washington, DC: The National Academies Press. doi: 10.17226/25473.
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Suggested Citation:"Chapter 8 - Effectiveness of Innovative Solutions." National Academies of Sciences, Engineering, and Medicine. 2019. Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff. Washington, DC: The National Academies Press. doi: 10.17226/25473.
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Suggested Citation:"Chapter 8 - Effectiveness of Innovative Solutions." National Academies of Sciences, Engineering, and Medicine. 2019. Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff. Washington, DC: The National Academies Press. doi: 10.17226/25473.
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Suggested Citation:"Chapter 8 - Effectiveness of Innovative Solutions." National Academies of Sciences, Engineering, and Medicine. 2019. Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff. Washington, DC: The National Academies Press. doi: 10.17226/25473.
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Suggested Citation:"Chapter 8 - Effectiveness of Innovative Solutions." National Academies of Sciences, Engineering, and Medicine. 2019. Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff. Washington, DC: The National Academies Press. doi: 10.17226/25473.
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100 This chapter shows the state DOT how to determine the efficiency and effectiveness of innovative compliance solutions. It provides state DOT practitioners with an overview of how watershed-based strategies can be used to achieve compliance with TMDL requirements. Previous chapters have identified effective treatment and management measures for each pol- lutant category. If state DOT practitioners are unable to meet TMDL requirements within the right-of-way due to cost, space, or other feasibility issues, watershed-based approaches may provide an alternative solution. There are two major categories of watershed-based approaches: pollutant equivalency methods and restoration of ecosystem services. Pollutant equivalency methods include stormwater banking, pollutant trading, payment in lieu, and off-site mitigation. In these approaches, pollutants are removed from other sources in the watershed to offset the excess pollutant load from the MS4. Restoration of ecosystem services generally refers to habitat restoration projects. This strategy offsets excess pollutant loads by improving the hydrology, geomorphology, and/or ecological processes within a degraded por- tion of a watershed. These projects often have multiple benefits for the entire watershed that go beyond offsetting loads. The compliance strategies for individual pollutants describe the applicability of on-site treat- ment measures based on pollutant characteristics. This section extends beyond the pollutant- specific compliance strategies identified to provide a state DOT with alternate options for compliance, with particular focus on trading programs. Since the department footprint within TMDL watersheds is typically minimal (<5 percent), a watershed-based compliance approach can be used. Incorporating regional compliance measures in conjunction with local munici- palities or stakeholders may also lead to a more effective and efficient water body solution. For various state DOTs—including Caltrans, North Carolina, and Nevada—these strategies provide a state DOT designer a wide array of options to consider when aiming to meet the water body targets and WLAs. Prior to the implementation of off-site compliance measures, a metric equivalency of compliance credits or loads removed for the funds allocated to local stakeholders should be developed and approved. The development of offset credits also requires quantification of the benefits of off-site mitigation compared to on-site control. Feasibility for State DOTs Strategies There are many watershed-based strategies that can be used to achieve compliance. A few of these strategies, all of which have been successfully implemented by at least one entity, are described in Table 49. The Watershed-Based Stormwater Mitigation Toolbox (WBSMT), C H A P T E R 8 Effectiveness of Innovative Solutions

Effectiveness of Innovative Solutions 101 which is described later in this chapter, can help state DOT practitioners evaluate and compare watershed-based compliance strategies for a given project, as well as for broader application to mitigate effects of multiple projects and of the highway network. Limitations The ability to institute watershed-based approaches depends on the flexibility of existing legal frameworks. Permittees are often subject to multiple levels of regulation, including at the local, state, and national levels. The Clean Water Act limits the revision of some effluent limitations under antibacksliding provisions included in Section 303(d)(4). States may limit public and private partnerships or the area in which off-site mitigation is applicable. If a TMDL is defined, EPA generally limits pollutant trading to within the watershed for which the TMDL has been approved. Specific NPDES permits with TMDL requirements may limit what approaches can be taken at a watershed scale. Toxic and persistent pollutants are typically not eligible for trading programs (EPA 2009B). Generally, EPA does not support trading where technology-based effluent limits exist or where drinking water systems may be affected by trading (EPA 2009B). Other legislation, such as the Endangered Species Act, may also influence the applicability of watershed-based approaches. Strategy Description Example Implementations Example Tools and Methodologies Pollutant Trading/ Stormwater Banking Credits are assigned for removal of a specific pollutant beyond what is necessitated by regulatory requirements. These credits can be sold to permittees who are unable to meet regulatory requirements for that pollutant. Volume-based treatment can also be traded in some jurisdictions, which can result in credits for multiple types of contaminants. Nutrient Trading by Municipal Stormwater Programs in Maryland and Virginia: Three Case Studies (Jones et al. 2017) Water Quality Trading (Oregon Department of Environmental Quality 2016) A Stormwater Banking Alternative for Highway Projects (McCleary 1999) Nutrient Tracking Tool (Tarleton University 2018) WinSLAMM (PV & Associates 2017) NutrientNet (World Resources Institute 2007) Off-Site Compliance Water quality control is instituted at a separate location within the same watershed to offset load reductions not met on site. Guidance for Developing an Off-Site Stormwater Compliance Program in West Virginia (Center for Watershed Protection 2012) NA Payment in Lieu Fees are paid to the permitting agency for permit load exceedances. The permitting agency uses these fees to construct public stormwater projects. Statewide Stream, Wetland, and Riparian Buffer Rates and Fees (North Carolina Environmental Quality 2018C) Guidance for Developing an Off-Site Stormwater Compliance Program in West Virginia (Center for Watershed Protection 2012) Nutrient ACM (North Carolina Department of Environmental Quality 2018A) Restoration/ Preservation Restoration projects are assigned a credit value. The completion of a restoration project can be used to offset debits accrued for not meeting water quality standards. Potential practices for crediting could include stream bed and bank stabilization, riparian buffers, in-stream enhancement, and floodplain reconnection (Clary et al. 2017). Ecosystem Credit Accounting System (Willamette Partnership 2018) Ecosystem Credit Accounting System: General Crediting Protocol Version 2.0 (Willamette Partnership 2017) Stream Restoration BMP Database: Version 1.0 Summary Report (Clary et al. 2017) Note: NA = not available. ACM = actual cost method. Table 49. Watershed-based compliance strategies.

102 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff In addition to regulatory limitations, the framework for watershed-based approaches can be difficult to establish and maintain. If a credit system is not already established within a state DOT’s jurisdiction, implementation of watershed-based approaches may be limited by cost, including funding positions to develop, institute, approve, and keep accurate accounts of credits. For these reasons, regulatory agencies may not be receptive to the idea of establishing or approving crediting systems. For agencies that wish to develop systems to support alternative compliance strategies, EPA has developed the Water Quality Trading Toolkit for Permit Writers, which provides guid- ance on how water quality trading can fit into NPDES permits and national (Clean Water Act) regulations (EPA 2009B). Feasibility Based on Pollutant Type Watershed-based approaches are more applicable to certain pollutants than others. Pro- tocols for off-site mitigation have been developed for TSS and nutrient constituents (EPA 2009B). For constituents such as bacteria and mercury, pollutant trading may be infeasible due to human health concerns. Metals and emerging contaminants may benefit from a watershed- based approach; however, there is limited precedent for establishing strategies. In cases where exceedances are strongly influenced by sources outside of the permittee’s control (for example, because of high contributions from soils or atmospheric deposition), trading programs may have limited success. Table 50 describes the advantages and limitations of traditional and inno- vative approaches based on pollutant type. Key Considerations of Trading Programs Engaging in watershed-based approaches requires DOTs to engage in a collaborative effort with watershed partners and use an existing framework or establish a new framework for evaluating equivalency of treatment methods. Establishing and Engaging Watershed Partners For a trading program to be successful, there must be enough permittees within a watershed who are able to exceed contaminant removal requirements (i.e., credit generators) and who can- not adequately meet contaminant removal requirements (i.e., credit buyers). However, partners can include nonpoint source dischargers so treatment by unregulated partners, such as agri- cultural producers, could generate a source of credits. Federal and state agencies—including research and extension services, the forest service, and similar agencies—could be valuable sources of data and partnerships. Lessons learned and protocols from compensatory mitigation programs (Section 404 of the Clean Water Act) may provide valuable insights and help identify project part- ners for state DOTs investigating off-site pollutant mitigation. Local governments may be willing to assist in or manage negotiation and contract development. It is also important to consider the proximity of potential partners to the project site, as this could affect trading ratios. The list of potential partners for restoration efforts is likely larger than for trading programs, as nonprofits, nongovernmental organizations, and research and education-oriented groups are often willing to assist in these efforts. For restoration project tracking and identification, some states—including Delaware, Maryland, Pennsylvania, and West Virginia—have established a tool called the Watershed Resources Registry (Watershed Resources Registry 2017). This inter- active mapping tool can help identify and compare sites that are important for preservation and that could benefit most from restoration. Similar tools could be useful in identifying both partnerships and potential projects.

Effectiveness of Innovative Solutions 103 Pollutant Source Control and Traditional BMPs Off-Site Mitigation or Credit Trading TSS Advantages • Removal is well understood and achievable. TSS can often be controlled using inexpensive source control measures. Many pollutants can be associated with TSS, so TSS removal can allow for multiple POCs to be addressed. Limitations • Space may be limiting. Fine particulates are difficult to remove. Advantages • Trading programs are explicitly supported per EPA guidance (EPA 2009B). Data are generally sufficient to support a trading analysis. Limitations • Equivalency of natural and anthropogenic TSS may be contested. TSS generated from highways may be associated with other pollutants, such as metals and hydrocarbons. Nutrients Advantages • Removal of TP and TN is well understood and can be achieved with applicable treatment processes. Limitations • Dissolved constituents may be difficult to remove. Source loading can vary greatly by season. Installation costs, space, and ongoing maintenance may be limiting factors. Advantages • Explicitly eligible for trading programs per EPA guidance (EPA 2009B). Data are generally sufficient to support a trading analysis. Examples of active and successful nutrient-trading programs exist. Limitations • Viable credits may be minimal if the watershed does not have substantial agricultural or wastewater discharges. Metals Advantages • Sources can often be identified. Particulate- bound metals are often efficiently treated by settling or filtration processes. Limitations • Installation costs and ongoing maintenance may be limiting factors. Advantages • Metals that are known to be present in background soils could be more effectively addressed with off-site mitigation practices. Limitations • Many metals are toxic, making them ineligible for trading programs (i.e., lead and mercury) (EPA 2009B). Not explicitly approved for trading but could be considered on a case-by- case basis. Bacteria Advantages • In watersheds with agricultural influence or wastewater discharges, state DOTs may represent a small fraction of a watershed’s bacteria load, which may require minimal on-site efforts to achieve compliance. Limitations • Fecal waste sources are difficult to track, and loading can vary by orders of magnitude. Advantages • Collaborative agreements may make TMDLs more achievable. • Off-site mitigation can target high-loading locations to achieve greater benefit. Limitations • Bacteria are generally ineligible for outright trading due to public health concerns associated with bacteria. Chloride Advantages • Most chloride is a result of traction control applications, so loading rates and timing are usually known. Source control measures are the most applicable control strategy. Limitations • Private property chloride applications cannot be controlled by state DOTs. • Chloride-based traction control is often dictated by public safety needs. Chloride can be toxic to vegetation. Space may be a limiting factor. Advantages • Partnership potential for state DOTs and private land owners to address total chloride load. • Training of local and private applicators. • Building salt barns for towns. Limitations • State DOTs may be able to treat for chloride only in key locations. • Not explicitly approved for trading but could be considered on a case-by-case basis. Traction control is often the largest source of chloride, which limits partnerships and available credits. Table 50. Comparison of traditional and watershed-based compliance strategies.

104 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff Major Elements of a Trading Program A crediting program must define baseline conditions, baseline requirements, trading ratios, methods for the calculation of credits, and methods for credit accounting and tracking (Samanns et al. 2015). • Baseline conditions: The reference condition, which may be the contaminant load at the time of program establishment, historical or pre-development load, load computed using a water quality standard, or a volume-based load. • Baseline requirements: The minimum requirements necessary to comply with applicable regulations (e.g., NPDES permit requirements or required BMPs). Once baseline require- ments are met, additional removal can generate credits. • Trading ratios: Factors applied to credits and debits that account for chemical, hydro- logical, and other environmental processes, as well as for inaccuracies and uncertainties in project success. These ratios ensure that credit and debit exchanges are fair and equivalent within the same watershed. Credits are not often traded on a 1:1 basis. Five categories of trading ratios are commonly used: Delivery, Location, Equivalency, Retirement, and Uncertainty (EPA 2009B). • Calculation of credits: Methods to convert pollutant removals and exceedances into trade- able credit values. Generation of credits is often predicted and planned using an approved tool that can calculate expected credit generation based upon structural or nonstructural BMP type. • Credit accounting and tracking: A framework for management and validation of transactions within a given credit bank, as well as for tracking long-term operation and maintenance plans. Quantifying the Success of Watershed-Based Strategies Several approaches can be taken to ensure that a watershed-based strategy is working as planned. Studies can be conducted to determine if water quality objectives are being met. While state DOTs may be involved and interested, monitoring outcomes is generally the responsibil- ity of regulatory and resource agencies. Program monitoring could include direct measurements of water chemistry, geomorphic measurements, functional assessment protocols, monitoring, or modules such as the International Stormwater BMP Database Stream Restoration Module (Clary et al. 2017). Where restoration projects are involved, tools such as a watershed health index can be useful (EPA 2018A). Watershed health indices consider six ecological attributes (landscape condition, habitat, hydrology, geomorphology, water quality, and biological condi- tion) and calculate index values that can be used to compare health within a group of water- sheds. However, such studies should account for potential countervailing trends and lags between the implementation of improvements and an observable ecosystem response. Examples of Successful Watershed-Based Approaches Samanns et al. (2015) identified water quality crediting programs present in 22 states and the District of Columbia. Each of these programs establishes a framework for trading nutrient credits; however, they vary in market structure, regulating entity, and pollutants considered. The following programs in North Carolina, Virginia, California, and Colorado represent established programs that can serve as a reference for other jurisdictions exploring watershed-based options. North Carolina Nutrient Offset Program The North Carolina Division of Mitigation Services operates a nutrient offset program that allows private and public entities to purchase nutrient (phosphorus and nitrogen) offset credits from a state-approved third-party nutrient credit bank. This program is used for the

Effectiveness of Innovative Solutions 105 Tar-Pamlico, Neuse River, Jordan Lake, and Falls Lake watersheds. A developer must either implement the on-site BMPs or join in a regional stormwater strategy before the offset nutrient options become available for buying or selling. The developer can use the nutrient load offsets to purchase the remainder of the load limitations not included in the on-site BMPs. Conditions are set for 8-digit and 10-digit hydrologic unit code (HUC) watersheds along with a requirement for developers to purchase offset nutrient credits from a state-approved third-party nutrient credit bank, if available. If private nutrient offsets are not obtainable, developers may pay a fee to the Nutrient Offset In-Lieu Fee Program to meet the nutrient (phosphorus and nitrogen) load reductions required. The North Carolina Division of Mitigation Services then becomes responsible for mitigating nutrient loads with watershed-based projects. If private nutrient off- sets are not obtainable, then developers may take a buy-down option in which an in-lieu fee is paid to the North Carolina Division of Mitigation Services, which then becomes responsible for mitigating nutrient loads with watershed-based projects (North Carolina Department of Envi- ronment and Natural Resources 2010). The buy-down portion of the program uses a third-party market structure or bilateral negotiations (North Carolina Department of Environment and Natural Resources 2010). During the 2016 to 2017 fiscal year, more than $700,000 was paid into the nutrient crediting program, representing reductions of more than 9,000 lb of nitrogen and 700 lb of phosphorus (North Carolina Division of Mitigation Services 2017). Virginia Department of Transportation Nutrient Crediting Program The Virginia Department of Environmental Quality Stormwater Nutrient Trading Pro- gram facilitates the purchase of nutrient credits by the Virginia Department of Transportation (Virginia DOT) for areas within the Chesapeake Bay watershed. In addition, the Virginia DOT solicits credits for purchase within specific watersheds of the Chesapeake Bay TMDL. For NPDES con- struction permits, the program sets eligibility requirements for purchasing credits based on dem- onstrating that on-site control has been considered to the “maximum extent practical,” that the size of the construction site is less than 5 acres, and that credits are available within the same HUC-8 watershed (Virginia Department of Transportation 2016). The Virginia DOT is responsible for direct negotiations on the purchase price with the credit producer. The department has estimated average cost savings of 51 percent when comparing construction and operational costs of nine on-site BMPs to water quality trading credits in the James River watershed (Nobles et al. 2014). California Department of Transportation Stormwater Compliance Program Within the Caltrans NPDES Statewide Stormwater Permit Attachment IV is a requirement that Caltrans invest in 1,650 stormwater mitigation units (acres of impervious or pervious area treated) a year to pursue measures addressing TMDL compliance (California State Water Resources Con- trol Board [SWRCB] 2012). Each compliance unit is defined as 1 acre of treatment and is set at a fixed-rate value of $88,000. This approach allows for maintaining a consistent effort state- wide on an annual basis, prioritizing implementation statewide, and normalizing WLAs for dif- ferent pollutants (California Department of Transportation 2015). Caltrans has implemented various strategies using stormwater compliance units, including on-site BMP retrofits, source control practices, and regional control efforts (California Department of Transportation 2015). California regulatory agencies—including EPA, the State Water Resources Control Board, and the nine Regional Water Quality Control boards—agreed that “acres treated” provided an objective TMDL compliance measure that is equivalent to the WLAs identified within the basin plan amend- ments of each TMDL. Caltrans has the flexibility to pursue projects with MS4 co-permittees. Caltrans can join other co-permittees within a listed TMDL watershed to pay into a BMP implementation project that pays a statewide rate of $88,000 per compliance unit (per acre treated). These regionwide, cross-jurisdictional watershed approaches are under way in several

106 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff major metropolitan areas, including the Bay Area (trash and mercury), Los Angeles water- shed programs, and the San Diego Water Quality Improvement Plans. California’s State Highway Operation and Protection Program 335 also funds off-site retro- fit projects, postconstruction BMPs, and maintenance activities for existing BMPs. Caltrans is taking a programmatic approach with co-permittees with the Cooperative Implementation Agreement to fund off-site stormwater quality BMPs located in watersheds with TMDLs. These Caltrans-funded BMPs generate credit for Caltrans to meet TMDL WLAs. Caltrans’ NPDES per- mit allows the department to transfer funds to the SWRCB to fund grants for co-permittees’ sup- port to assist Caltrans with TMDL compliance. Caltrans receives credit to offset TMDL WLAs. Compliance credits can be achieved for stormwater BMP and monitoring program-related retrofits, other monitoring efforts that lead to successful cooperative implementation for TMDL compliance, and postconstruction treatment beyond permit requirements. Additional pollution- reduction controls, such as hot spot litter pickup and street sweeping, are under consideration for implementation to accompany the brake pad–copper reduction partnership that has existed for more than a decade. Benefits of Caltrans Alternative Compliance Approach (Abbasi and Koskelo 2013): • Annual cost is fixed by predetermining the number of required compliance units and cost per unit. • It provides working alternatives to comply with performance and design requirements. • Compliance is established through annual funding of an in-lieu fee-type program and pur- chasing compliance units. • MS4 co-permittees are responsible for implementing watershed improvements using Caltrans funding. • Caltrans operates and maintains the compliance tracking system but is not responsible for long-term maintenance of watershed improvements. • Caltrans is dependent on stormwater co-permittees to implement watershed improvements correctly and on time. Colorado Department of Transportation Permanent Water Quality Mitigation Fund The Colorado Department of Transportation (Colorado DOT) contributes $6.5 million per year to a Permanent Water Quality Mitigation Pool that is managed under Colorado’s New Development and Redevelopment Program (Colorado Department of Transportation 2015). These funds are used to construct structural BMPs to achieve water quality improvement goals. A prioritization process determines which projects are funded based on environmental impact study requirements and discharging to 303(d)-listed or priority water bodies. The revolving fund is required to be 80 percent spent within a 3-year time frame. All projects are independently selected and managed by Colorado DOT. If a project is classified as a Priority Project, then permanent stormwater quality control measures must be constructed on site to treat impacts from the new impervious portion of the project. Three possible triggers are identified for a project to be designated a Priority Project. These projects must comply with respective design standards: • Environmental Assessment–Environmental Impact Statement Priority Trigger: Project increases the impervious area by 20 percent or more and an environmental assessment or environmental impact statement is required. • 303(d) Priority Trigger: Project increases the impervious area by 20 percent or more and discharges to a 303(d) segment listed for arsenic, chloride, chromium, copper, manganese, zinc, or TSS.

Effectiveness of Innovative Solutions 107 • Cherry Creek Reservoir Drainage Basin Priority Trigger: Any portion of a project dis- charging to the Cherry Creek Reservoir Drainage Basin is a Priority Project. Nutrient Bank/Nutrient Credit Registry Nutrient banking is an alternative compliance program whereby designated nutrient credits are produced in watersheds or trading areas that result in a surplus of load credits after baseline conditions are met. Credits result from BMP installation or reconstruction that provide surplus treatment, implementation of agricultural conservation practices (i.e., buffer strips, no till, and so on), or the conversion of agricultural property back into natural areas. The purchase of credits by state DOTs is reported back to the state regulatory agency to achieve compliance for the TMDL. Other Examples The Environmental Trading Network provides a comprehensive collection of existing and planned water quality trading and other environmental market-based programs (Keiser & Asso- ciates, LLC 2018). The website organizes information (including links to pertinent information) by state and watershed and provides a map of water quality trading projects and programs. A list of known trading organizations and tools that could be useful to those looking to institute a water quality trading program in their jurisdiction is also provided. Comparing On-Site and Off-Site Approaches This section shows state DOTs how to compare on-site and off-site BMPs to watershed approaches for compliance. Appropriate methods for comparing on-site BMPs to off-site treat- ment depend on the types of approaches considered. When off-site compliance uses structural BMPs (in-kind approaches), the cost and performance evaluation techniques described in Chapter 6 and Chapter 7, respectively, are applicable. Off-site compliance using conservation- or restoration-based approaches requires development of a framework for comparing the benefits of disparate (out-of-kind) practice types. The WBSMT provides a methodology and associated tool for comparing in-kind and out-of-kind approaches (Weinstein et al. 2017). Regardless of approach, comparing the benefits of on-site and off-site water quality treatment is inherently complex due to the multitude of factors to consider. The following are important considerations when comparing on-site and off-site mitigation approaches: • Treatment location prioritization: Benefits are dependent on both proximity to receiving waters and magnitude of treatable pollutant loads or equivalent environmental benefit. • Cost–benefit analysis: Factors including treatment volume, performance, implementation cost, and maintenance cost are all important considerations for structural BMPs. Comparing structural BMPs to restoration-based practices requires a methodology for ranking project preferences or quantifying economic, environmental, and social benefits. • Leveraging partnership goals: Joint funding efforts, project size, and targeted treatment for individual POCs may all be influenced by economies of scale. Key Resources There are many resources available to state DOT practitioners looking for more infor- mation with regard to watershed-based approaches. FHWA sponsored a feasibility study for stormwater quality trading that is a comprehensive qualitative resource on this subject (Samanns et al. 2015). The study explored the possibility of state DOTs engaging in or estab- lishing crediting and trading systems. From a quantitative perspective, the WBSMT provides a proof of concept on how to directly compare project-specific watershed-based approaches (Weinstein et al. 2017).

108 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff FHWA Feasibility Study The FHWA Feasibility Study for the Development of a Frame work for an Effective Stormwater Quality Credit/Banking/Trading System provides state DOT-oriented guidance on how to imple- ment a water quality crediting program (Samanns et al. 2015). This study • Includes conclusions from an interview with 12 stakeholders already involved in water quality trading programs, • Describes program drivers and components, • Provides examples of existing programs, and • Describes the feasibility and key considerations for future state DOT programs. The most feasible programs for state DOTs are noted to be nutrient banking/credit registries, third-party agreements (e.g., out-of-kind mitigation or in-lieu fees), or other alternative compliance programs, such as internal exchange, where equivalent treatment is provided on another state DOT project within the same watershed. Watershed-Based Stormwater Mitigation Toolbox The WBSMT was developed as part of NCHRP Research Report 840 and provides a use- ful reference for state DOTs interested in understanding off-site and out-of-kind treatment approaches and comparison methodologies (Weinstein et al. 2017). The associated tool uses a Microsoft Excel spreadsheet environment to compare on-site and off-site, in-kind and out- of-kind, and in-lieu fee/bank strategies for a given site. The tool leverages national data sets for these evaluations but allows for local inputs when information is available. Evaluations are applicable to planning-level analyses by considering beneficial uses, desired ecosystem services, and watershed processes. The tool uses an eight-step process, with the first seven steps requiring the user to input and review assorted information and weighting factors to establish these planning-level estimates. Information required to use the tool includes the hydrologic soil group for the project site and potential offsite areas, long-term volume and load reduction targets, and stormwater BMP capture and volume-reduction design basis (often specified by regulations). The eight steps of the process are the following: 1. Enter project details. 2. Enter watershed characteristics, based on HUC-12. 3. Establish pollutant load-reduction targets. 4. Input preferred BMP design parameters for in-kind, on-site treatment. 5. Input tributary area and preferred BMP design parameters for in-kind, off-site treatment. 6. Input out-of-kind mitigation option preferences. 7. Review target load reductions and mitigation priorities. 8. Evaluate results. Results are given as priority scores based upon four assessments: • Watershed processes based on ecosystem services, • Watershed processes based on unmitigated loads, • Watershed processes based on stormwater management goals, and • Opportunities based on surrogate land uses. Additional steps are included for advanced users to assist in tailoring results to a given location. Figure 28 illustrates an example output that can be obtained from the WBSMT. This exam- ple, which is based on a hypothetical site and uses default parameters for illustration purposes only, shows that in-kind BMPs (both on site and off site) are able to exceed the percent total

Effectiveness of Innovative Solutions 109 load reduction (%TLR) targets for volume, TSS, and TN, but are unable to meet the TP %TLR target. Therefore, there is an outstanding % TLR that must be met with out-of-kind mitigation measures. Out-of-kind measures may include a variety of watershed improvement techniques, but the measures included in the WBSMT include stream restoration, upland stabilization, impervious surface disconnections, and wetland restoration or creation. The WBSMT provides an initial estimate of the potential area required for these out-of-kind measures to provide an equivalent benefit to the watershed as compared to direct load reductions. The user has the option to choose self-implementation or in-lieu implementation of the out-of-kind measures. Self-implementation means that the state DOT would be responsible for identifying and com- pleting the mitigation project. In-lieu implementation means that the state DOT would pay into an established in-lieu program. Hence, the latter only applies if such a program exists and may require an additional multiplier (the default multiplier for the WBSMT is 1.1). For more information on the computational methods and for a detailed example application of the WBSMT to a state DOT project in Pierce County, Washington, see NCHRP Research Report 840 (Weinstein et al. 2017). In Kind On Site In Kind Off Site Self-Implemented Out of Kind In Lieu Out of KindMitigation Measure Footprint Area Summary Figure 28. Example of output generated by the watershed-based stormwater mitigation tool.

110 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff While the WBSMT provides a proof-of-concept for comparing and evaluating on-site versus off-site and in-kind versus out-of-kind approaches for addressing TMDL WLAs, the type and extent of out-of-kind practices depend on the factors of safety and mitigation ratios that are accepted by the regulatory authorities when considering equivalency of approaches and uncer- tainty of the methods and data. In the example output shown in Figure 28, which uses default values in the WBSMT tool, a relatively small amount of stream improvement could potentially meet the outstanding phosphorus %TLR. However, additional analysis and site-specific data collection would be required to demonstrate that any out-of-kind practice could meet the miti- gation objectives. Water quality crediting for stream and wetland restoration projects is still in its infancy in both the methods and data necessary to estimate pollutant load reductions, as well as the regulatory policies and programs that allow such credits to be applied toward TMDL compliance. The Chesapeake Bay Program is perhaps the most mature and unique example of a plan that has developed stream restoration crediting approaches for nutrient TMDLs (Schueler and Stack 2013). These crediting approaches have been recently incorporated and expanded into a national stream restoration crediting guidance document (Bledsoe et al. 2016), which could be used as a starting point for other TMDL programs interested in pursuing stream restoration as an out-of-kind approach to addressing TMDLs.

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State DOTs are increasingly subject to Total Maximum Daily Load (TMDL) requirements for water quality improvement that are implemented through National Pollutant Discharge Elimination System (NPDES) permits.

As a result, state DOTs may incur significant costs to construct, operate, maintain, and monitor performance of best management practices and other stormwater treatment facilities that treat stormwater from sources outside the right-of-way, as well as stormwater from roadway sources.

TRB’s National Cooperative Highway Research Program (NCHRP) Research Report 918: Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff describes how to evaluate TMDLs and develop a plan to comply with the requirements of a TMDL. The methods provide a robust approach to determining the pollutants of concern and how to assess the contribution of the roadway while understanding other important factors that affect overall pollutant loads, including adjacent land uses and watershed conditions and characteristics.

A set of presentation slides summarizing the project that developed the report is available for download.

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