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

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43 This chapter shows the state DOT how to develop pollutant-specific compliance strategies. It provides practitioners with a conceptual approach that can be integrated into the TMDL plan- ning process. The individual pollutant compliance strategies are sequential based on the steps identified below. 1. Identify the primary POC. Compliance strategies are organized by pollutant type based on the identification of impaired water bodies or implemented WLAs. 2. Identify the source of pollutants in the roadway environment. Individual pollutant character- istics, source, and transport were described in Chapters 2 and 3. Runoff concentrations were developed based on the land use loading rate analysis. 3. Compare treatment options for either on-site planning track or off-site planning track. 4. For on-site planning track, identify the applicable unit treatment processes (UTPs) for the POC(s). A review of treatment methods for the specific pollutant is provided based on a comparative analysis of treatment options. a. Compare on-site treatment measures. The practicability, landscape requirements, and treat- ment performance of applicable structural BMPs and nonstructural controls are described using screening matrices. The reasons for excluding certain practices are also explained. 5. Determine the feasibility of off-site planning track. Considerations for alternative compliance measures to structural controls that effectively address the pollutant are analyzed (see Chapter 8). Understanding Pollutants of Concern A comparison of on-site and off-site treatment measures for performance, safety, practicality, and feasibility is discussed in Chapter 8. As discussed in Chapters 3 and 6, understanding the POCs is key to determining the compliance strategies that can support state DOTs in implementing appropriate measures to address TMDLs. Figure 2 (TMDL Review Process Flow Chart) provides a brief understanding of the approaches that state DOTs should consider through the planning and implementation phase. Once a POC has been determined based on an implemented TMDL or water body impairment (see Chapter 2), pollutant-reduction strategies can be developed to reduce the POC loads. Strategies may include specific pollutant-based compliance measures and watershed-based approaches. The identification of specific pollutant categories (see Chapter 2) and a statewide pollutant category-based compliance strategy is beneficial for a state DOT since state DOTs are a nontraditional MS4 entity and can be subject to many TMDLs throughout the state requiring unique compliance strategies. A consistent compliance approach statewide can be an advantage for the stormwater practitioner at state DOTs and other transportation agen- cies, since approaches previously used in other impaired watersheds that are effective can lead to appropriate control of the primary pollutant sources from highways. In addition, consistency in compliance approach gives state DOTs the capability of applying their resources to projects and treatment controls that are proven effective for the specific POC. C H A P T E R 4 Compliance Strategies Approach

44 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff Pollutant-based compliance strategies provide a more effective implementation of control measures that are geared toward watershed benefit. Compliance strategies are focused on estab- lishing mitigation measures based on the primary POCs for highway runoff. TMDL WLAs and implementation plans should be based on expected source contributions and accurately reflect state DOT impacts and water quality mitigation capabilities. Strategies should ensure that the responsibility placed on state DOTs is commensurate with department contributions to the receiving water body impairments and actual watershed loads. The process starts with determin- ing the POC and identifying the corresponding treatment options for those pollutants, such as institutional controls, structural retrofits, or watershed stakeholder collaborative activities (e.g., wetland restoration) (Figure 20). Compliance strategies can be determined based on the state DOT’s POC and may be independent of the WLA analysis. The information from previous tasks is designed to help guide state DOTs if alternative approaches to TMDLs are viable. For each pol- lutant group (sediments, nutrients, metals, bacteria, and chlorides), relevant source controls and treatment processes are discussed based on a description of the pollutant characteristics, sources, and transport mechanisms. Specific contaminants relevant to roadway runoff are described for each pollutant group. One approach for selecting treatment options is to identify the UTPs applicable for the tar- get pollutant based on constituent source, form, and chemical speciation. UTPs are physical, chemical, or biological treatment processes used for water treatment that can either stand alone or be incorporated into a larger treatment train. Understanding the UTPs applicable to the treatment of the POC is a critical step in selecting and designing effective practices. This section is intended to provide planning-level guidance to assist state DOT practitioners in determining treatment options for a specific contaminant. Comparisons of treatment BMP costs and effec- tiveness are further elaborated in Chapter 7. Regardless of pollutant type, a stepwise process is useful when developing a compliance strategy. Figure 20 demonstrates the steps involved in the process. 1. Identify POC: The first step in developing a compliance strategy is to identify specific causes of the impairment (see Chapter 2). The causes may include one or several pollutants that are identified in TMDL WLAs, municipal regulations, or anticipated future concerns. 2. Determine POC sources and characteristics: An understanding of the source and transport mechanisms of a specific contaminant is critical to determine the most effective treatment Off-Site Planning Track 1. Identify POC 2. Determine POC Sources and Characteristics 4. Identify Applicable UTPs 3. Compare Mitigation Options On-Site Planning Track 5. Compare On-Site Treatment Options Chapter 8 Figure 20. Compliance strategy identification process.

Compliance Strategies Approach 45 strategies. The pollutant source, partitioning, and speciation impact the selection of a compli- ance strategy: a. Source: Some sources are easily identified and directly controllable by the state DOT, while others are not. Sources that originate from within the state DOT right-of-way are generally easier to control. Anthropogenic and natural sources can deposit pollutants in the roadway environment (see Chapter 3). Pollutant sources vary for different POCs, including atmo- spheric deposition, land use, vehicle use, adjacent soils, traction and deicing application, and animal and human waste. An understanding of the pollutant source and location within the roadway corridor and watershed impacts the effectiveness of source control versus structural practices and the optimal location for treatment. b. Partitioning: Some pollutants can be transported in both dissolved (aqueous) and particu- late forms with washoff characteristics determined by the pollutants’ solubility properties and source. Depending on particle size gradation, particulate-bound pollutants can be removed by physical processes, such as sedimentation and filtration (Figure 21). Dissolved constituents— typically measured through a 0.45 µm filter—are more difficult to remove and often require chemical or biological mechanisms or source control approaches for removal (Figure 24). c. Speciation: Speciation refers to the composition of the dissolved fraction. Dissolved con- stituents can be present in either ionic form or complexed with other constituents, such as dissolved organic matter. Speciation is dependent on runoff chemistry (i.e., pH, ionic strength, and dissolved organic matter), hydrologic conditions, and pollutant characteris- tics (Gnecco et al. 2008, Strecker et al. 2005). Understanding the biological and chemical transformations necessary to immobilize the target pollutant is needed to select an appro- priate treatment process. 3. Compare treatment options: After the pollutant source has been identified, the treatment options that specifically target the POC can be compared. Potential treatment options include off-site mitigation, structural BMPs, and source controls. A compliance strategy is created by selecting an appropriate grouping of treatment options to address the POC. Further meth- odologies for comparing treatment options based on performance and cost are described in Chapters 6 and 7, respectively. (Note: Step 4 is discussed later in this chapter). Treatment Options Off-Site Mitigation Off-site mitigation may be selected when space and time are of critical concern, when sources are dispersed and difficult to control, or when the off-site alternative presents a greater benefit to Sediment Nutrients Metals Bacteria Chloride Gross Solids (>5000 µm) Screening Coarse to Medium (125 to 5000 µm) Sedimentation Fine Particulates (10 to 125 µm) Filtration Very Fine/Colloidal (0.25 to 10 µm) Sorption Dissolved (<0.45 µm) Source Control, Sorption, Biological Uptake Pollutant of ConcernParticle-Size Gradation Example Effective Treatment Process Figure 21. Treatment processes for POCs based on particle-size gradation.

46 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff the watershed. In addition, proximity to receiving waters, magnitude of TMDL exceedance, and cost are important considerations when comparing on-site and off-site mitigation strategies. More information on off-site mitigation strategies is presented in Chapter 8. Structural Best Management Practices Structural BMPs are facilities designed to convey, detain, and treat stormwater runoff. They are selected based on their effectiveness in directly addressing a specific POC or suite of pol- lutants included in the design. Structural BMPs may be linked in series to create a treatment train, with varying UTPs addressed within treatment components. In addition to treatment efficiency, structural BMP designs should also consider aesthetic, cost, maintenance, safety, and space requirements. Seven common structural BMP types that could be evaluated include the following: • Solids Removal Devices: Screening, gravity settling, or centrifugal forces used to remove debris and coarse sediments from the flow line. • Detention Basins: Surface storage facilities—sometimes vegetated—for the temporary deten- tion of stormwater to attenuate flows. Flow attenuation reduces stream energy and extends the discharge hydrograph to allow more dilution during storm events. • Vegetated Conveyances: Vegetated swales or filter strips with optional amended soil that treat shallow sheet flows through filtration and infiltration of low flows. • Infiltration Facilities: Basins, vaults, or trenches that are designed to temporarily store a defined volume of runoff until it can be infiltrated. • Media Filters: A variety of configurations that use a bed of sand or engineered media to filter stormwater runoff. • Porous Pavement: A permeable surface course and subsurface storage layer providing deten- tion and filtration. Captured runoff is either infiltrated or collected and discharged through an underdrain. • Permeable Friction Course (PFC): An aggregated mixture of porous material with an open void structure that allows infiltration and drainage of surface water, providing treatment of the runoff. • Bioretention: Shallow vegetated depressions with planting layer providing filtration, vegetated treatment, detention, and often infiltration of captured runoff. • Wet Ponds and Wetlands: Surface depressions—possibly vegetated—with designed wet zones that provide detention and treatment of surface runoff. Source Controls Source controls are nonstructural practices that directly prevent runoff of the POC from the pollutant source. Critical to the efficacy of a source control practice is correct identification of the source within the roadway environment. Nonstructural source controls include pollution reduc- tion measures, cleaning efforts, landscape alterations, and management plans. Source control practices applicable to the roadway environment that could be evaluated include the following: • Street Sweeping: Routine use of vacuum or mechanical sweepers to remove the accumulated sediment and debris from the road surface. • Catch-Basin Cleaning: Routine cleaning of accumulated sediment and debris from catch basins with a designed sump. • Natural Landscaping: Buffer controls and impervious area reduction or disconnection to reduce runoff volumes. • Vegetation Management: Mowing, vegetation removal, or planting plans designed to mini- mize leaf fall on the roadway or increase the surface roughness of flow pathways to improve runoff treatment.

Compliance Strategies Approach 47 • Erosion Control: Vegetation coverage, slope and outfall protection, and construction BMPs to prevent sediment release from erosion. Refer to erosion and sediment control guidance manuals for specifics on this category (AASHTO Center for Environmental Excellence 2017). • Material Management: Removal or prevented use of construction or vehicle materials that result in polluted runoff. Managing fertilizer application rates and timing is also a materials management control strategy for reducing nutrient sources. • Spill Prevention and Response Plans: Containment zones and response initiatives for the control of oils and other contaminants spilled at operational facilities. • Traction Control Plans: The use of alternative materials, scheduling, or application rate reduction of salts and sand in cold weather climates to reduce chloride and sediment road- way loading rates. • Anti-Icing Management: The use of alternative materials or scheduling to address chloride contamination in surface runoff. Modifying application techniques may also enhance the capabilities of this control. • Covering and Containing Stockpiles: The use of coverings and other containment mea- sures on construction and traction control materials—including road sands and road salt— to prevent washoff during rainfall. • Public Education on Littering: Signage, fines, and outreach campaigns to improve public awareness about littering. State DOTs should also promote public involvement for programs such as litter pickup and Adopt-a-Highway—particularly in high trash-generating areas— and encourage state police to enforce littering laws. The potential source controls applicable to the POC can be determined using Table 21. The effectiveness of a given source control depends on the degree of change enacted and proximity Source Control Type Pollutant Addressed Volume Reduction Coarse Debris Sediment Oil and Grease Nutrients Organics Metals Bacteria Chloride Street Sweeping – 2 2 – 1 1 1 1 – Catch-Basin Cleaning – 2 2 – 1 1 1 1 – Vegetation Management 1 1 2 – 1 2 – – – Erosion Control – 2 2 – 1 1 1 – – Natural Landscaping 2 – 1 – 1 1 1 1 – Material Removal/ Prevention – – – – – – 2 – – Traction Control Plans – – 2 – – – – – 2 Public Education on Littering – 2 1 – 1 1 1 2 – Spill Prevention and Response Plans – – – 2 2 – 2 – – Anti-Icing Management – – 1 – 1 – 1 – 2 Covering and Containing Stockpiles – 2 2 – 1 – 1 – 2 Note: – = source control does not address this pollutant; 1 = source control does not directly address this pollutant but may have marginal effectiveness; 2 = source control can be developed to directly address this pollutant. Table 21. Pollutants addressed by source control type.

48 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff to the pollutant source. Source control considerations for specific POCs are further elaborated on in the discussion of individual pollutant compliance strategies. 4. Identify Applicable UTPs: Based on the source, partitioning, and speciation of the POC, the applicable UTPs can be identified. UTPs can be organized according to four fundamental process categories (Table 22) (Huber et al. 2006): a. Hydrologic Operations: Structural practices with a storage component can impact the hydrologic cycle by detaining (flow alteration) or retaining (volume reduction) stormwa- ter runoff. Low-impact development (LID) principles aim to implement control measures that result in matching the rate, volume, and duration of runoff to the predevelopment condition. Nonstructural controls that incorporate LID principles—such as disconnect- ing impervious areas, preserving vegetation, and conserving natural topography—can also have hydrologic benefits. Detention results in a reduction in peak discharge by implementing either conveyance systems that increase runoff travel time or rate-controlled storage facilities. By increasing residence time, water quality may be improved by providing time for other treatment processes, such as sedimentation, to occur. The permanent capture of stormwater runoff by infiltration, evapotranspiration, or capture and reuse reduces pollutant loading by reducing the total runoff volume. The use of infiltration as a stormwater treatment process is effective for all POCs, except highly mobile pollutants—such as chloride and nitrate—that can cause direct impacts on groundwater and reemerge in baseflow of streams. Infiltration feasibility and overall effectiveness at mitigating impacts on receiving waters via infiltration are dependent on available space, soil type, groundwater depth and connectivity to surface waters, existing soil and groundwater contamination, geotechnical constraints, and existing infrastructure constraints (Strecker et al. 2015). Infiltration capacity is dependent on system storage volume and surrounding soil conditions. The possibility of groundwater and vadose zone contamination should be evaluated when considering stormwater infiltration. Runoff with elevated concentrations of mobile pollutants—such as nitrate and chloride—increases the risk of soil and groundwater contamination and release to surface waters via soil erosion, interflow, and baseflow for these constituents. The use of vegetated systems—such as swales and bioretention basins—can promote evapotranspiration losses. b. Physical Treatment: Physical treatment processes can remove particulate-bound pollut- ants through straining, filtration, or separation processes. Pretreatment devices—including screens, nets, filters, and hydrodynamic separators—can remove coarse sediment and reduce the clogging risk of downstream practices. Entrapment of smaller particle sizes can be achieved by media filtration. Gravitational forces can be used to remove suspended sediments via separation and sedimentation processes in detention facilities. Physical processes can also target nonparticulate pollutants in specific instances. Exam- ples include aeration systems to increase dissolved oxygen concentrations and to remove volatile compounds and ultraviolet disinfection for bacteria removal. c. Biological Processes: Biological processes include microbially mediated transformations and plant uptake and storage. Microbially mediated transformations can include oxidation- reduction reactions by bacteria, algae, and fungi through metabolism, organic material decomposition, inorganic transformations, and degradation of foreign substances. The occurrence of specific oxidation-reduction reactions depends on the reaction reduc- tion potential and the presence of specific compounds and microbes. Oxygen-depleted (anaerobic) environments in stormwater BMPs can promote the transformation of inorganic compounds into less-soluble forms. Plants can accumulate nutrients, metals, and organic compounds through diffusion of ions into the root systems, which are transported and stored in plant shoots. Some spe- cies are capable of accumulating high concentrations of a specific constituent, known as

Fundamental Process Category UTP Operational Components Pollutants Treated/Controlled Coarse Debris Sediment Oil and Grease Nutrients Organics Metals Bacteria Chloride Hydrologic Operations Flow Alteration Peak flow reduction (detention) Xa Xa Volume Reduction Infiltration, evapotranspiration, or reuse (retention) X X X X X X X X b Physical Treatment Screening Size separation & exclusion X Filtration Size separation & exclusion X X X X X Separation Density, gravity, or inertial forces X X X Aeration Volatilization X Natural Disinfection Ultraviolet light X Biological Processes Microbially Mediated Transformations Oxidation-reduction reactions X X X X Uptake and Storage Bioaccumulation X X X Chemical Processes Sorption Surface complexation andprecipitation X X X X Ion Exchange Cation exchange capacity X X Coagulation/ Flocculation Solid formation X X Chemical Disinfection Chemical agents (chlorine/ozone) X aNot directly removed by the flow alteration but can provide indirect control by reducing mobility and improving effectiveness of other treatment processes. bChloride removal is temporary and eventually migrates to groundwater or reemerges in hydrologically connected surface waters. Table 22. Pollutants treated by unit treatment process.

50 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff hyperaccumulators (Salt et al. 1998). When using plants in treatment systems, harvesting may be necessary to prevent reentry of pollutants after decomposition (Davis et al. 2010). The presence of vegetation can also improve the hydrologic performance of a media filter system by establishing root macropores that increase infiltration and reduce clogging potential (Le Coustumer et al. 2012). This chapter provides additional guidance on compliance strategies that use biological processes. Additional considerations and guidance on the control of metals within the highway environment can be found in NCHRP Report 767 (Barrett et al. 2014). d. Chemical Processes: Chemical reactions within a stormwater practice can occur within the water column and at the surface of filter media. The speciation of the POC and run- off chemistry impacts the occurring chemical processes and dictates the needed UTP. Sorption refers to the net removal from solution of a constituent at a media surface via physiochemical adherence or bonding. Sorption is the collective group of surface inter- actions, including adsorption, surface complexation, ion exchange, and precipitation. Sorption is influenced by the surface structure and particle size of a filter medium. Media with many surface functional groups (e.g., carboxyl and hydroxyl groups) and a high cation exchange capacity have a higher sorption capacity (Sparks 2003). Organic matter generally provides the bulk of cation exchange capacity in natural soils, and the addition of organic matter such as compost, peat, and mulch can improve filter media performance (Bradl 2004, Paus et al. 2014). Media amendments—such as iron filings, fly ash, zeolite, granulated activated carbon, and other carbon sources—have been shown to promote removal of specific nutrient and metal constituents (Erickson et al. 2012, Genç-Fuhrman et al. 2007, Zhang et al. 2008). The sorption capacity (mg/kg) of a medium to retain a specific compound can be measured using equilibrium isotherm models (Genç-Fuhrman et al. 2007, Wium-Andersen et al. 2012). Flocculation and coagulation is the process of converting dissolved constituents and non- settleable solids to solid sludge. Dependent on particle properties, mixing, and runoff chem- istry, natural coagulation occurs in stormwater basins. Advanced treatment using chemical additions can induce precipitation, coagulation, and flocculation of certain dissolved constit- uents. When advanced treatment is needed but not feasible in stormwater BMPs, runoff may be diverted to an existing wastewater treatment plant for chemical treatment. The feasibility of this solution is dependent upon the proximity of a wastewater treatment plant, as well as receiving a permit, plant capacity, and interference with plant operations and performance. Chemical disinfection refers to the mitigation of stormwater-borne pathogens using chemical agents such as chlorine, silver, copper alloys, or ozone. Chemical agent disinfec- tion provides an alternative to natural disinfection for pathogen treatment. The use of chemical treatment in a stormwater practice must account for effects on the downstream ecosystem. Similar to flocculation treatment, diversion to a wastewater treatment plant may be suitable in certain situations. A summary of applicable UTPs for treatment of various constituents is provided in Table 22. Refer to Huber et al. (2006) for detailed descriptions of the included treatment processes. Upon identification of required UTPs to treat a POC (Table 22), an initial screening of appropriate struc- tural BMPs can be completed by identifying structural BMPs with the needed UTPs (Table 23). Several BMP types may address one UTP, and selection of a specific BMP type depends on site constraints and pollutant removal efficiency for the POC. Design components and pollutant- specific UTPs are further elaborated on in the individual pollutant compliance strategies. Determining Compliance Strategies Pollutant-based compliance strategies are analyzed for a more effective implementation of control measures that are geared towards watershed benefit. Compliance strategies focus on

Compliance Strategies Approach 51 establishing mitigation measures based on primary pollutants of concern for highway runoff. These strategies ensure that the responsibility placed on state DOTs is commensurate with department contributions to the receiving water body impairments and actual watershed loads. A variety of compliance approaches—such as institutional controls, structural retrofits, or watershed stakeholder collaborative activities (e.g., wetland restoration)—are identified for the given pollutant category. Sediment TMDL Control Strategies Properties. Sediment in roadway runoff can be characterized by particle size distributions (Kim and Sansalone 2008). Particle sizes can vary from gross solids composed of trash and debris to fine or colloidal solids with diameters less than 1 µm (Table 24). Particles in runoff are pre- dominantly inorganic, such as quartz and calcite with clays and organic constituents adsorbed to the surface (Huber et al. 2006). Other pollutants—including bacteria, metals, organics, and nutrients—can be adsorbed to particles and sediment removal, or source control can be a con- trol strategy for other particulate-bound contaminants. For example, the organic contaminant groups polychlorinated biphenyls (PCBs) and polyaromatic hydrocarbons (PAHs), which are often regulated to low microgram-per-liter concentrations within state DOT jurisdictions, are carried by sediments due to their insolubility. Common sources of PAHs include motor vehicle exhaust, smoke, and certain types of asphalt sealants. PCBs are found in electrical equipment, motor oil, thermal insulation, and adhesives. Hwang and Foster (2006) found that 68 percent to 97 percent of PAHs in stormwater runoff were associated with particles, and PCBs partition similarly. Thus, sediment control strategies apply to removal of these contaminants. Structural BMP Type Unit Treatment Process (UTP) Hydrologic Physical Biological Chemical F lo w A lt er at io n V o lu m e R ed u ct io n S cr ee n in g F ilt ra ti o n S ep ar at io n A er at io n N at u ra l D is in fe ct io n M ic ro b ia lly M ed ia te d T ra n sf o rm at io n s U p ta ke a n d S to ra g e S o rp ti o n Io n E xc h an g e C o ag u la ti o n – F lo cc u la ti o n C h em ic al D is in fe ct io n Solids Removal Devices – – 3 – 2 1 – – – – – – – Detention Basins 3 1 – – 3 – 2 2 1 1 1 1 – Vegetated Conveyances 2 2 – 2 1 1 1 1 1 1 1 – – Infiltration Facilities 3 3 – 3 1 – 1 1 1 1 1 – – Media Filters 2 2 – 3 1 – 1 2 1 3 3 – 2a Biofiltration 2 2 – 3 2 – 2 2 2 3 3 – – Wet Ponds and Wetlands 3 1 – 2 3 2 2 3 3 2 2 1 – Note: – = BMP type does not include this UTP; 1 = BMP includes UTP but not explicitly in design and likely has marginal effectiveness; 2 = BMP may effectively include this UTP if necessary design components are included; 3 = BMP specifically designed for the UTP. aProprietary media filters. Anti-microbial products may be restricted by pesticide regulations in some states. Table 23. Unit treatment processes effectiveness based on structural BMP type.

52 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff Due to an increase in surface area, smaller sediment fractions carry the majority of other particulate-bound pollutants (Morquecho and Pitt 2005). Runoff particle size distributions and material properties vary from site to site based on hydrology, anthropogenic inputs, and in situ soil types (Kayhanian et al. 2012). Runoff sediment concentrations can be characterized by measurements indicative of different particle size fractions and organic content. Though monitored constituents can vary, the critical aspect for developing control strategies is the targeted particle-size diameter. Gross solids, settle- able solids, and fine solids are associated with applicable treatment strategies (Table 24). Likely, each of these size fractions are present in roadway runoff. Targeted source control strategies and treatment measures can reduce specific size fractions. The treatment train approach can be used to address the complete suite of sediment-size fractions. Sources. Sources of sediment in roadway runoff include both natural sources—such as deposition and washoff of adjacent soils—and anthropogenic sources, such as vehicle traffic and urban activities. The ability to control the inputs of sediment to the roadway varies based on the source (Table 25). If a source is identified as controllable or partially controllable in Table 25, source control practices may be an effective strategy for reducing associated sedi- ment loads. Treatability. When source control practices are deemed insufficient for sediment control, physical treatment processes can be used by designing applicable structural BMPs. The removal of solids from runoff is a function of density, particle size, and shape (Clark and Pitt 2012). The UTPs of screening, sedimentation, and filtration are applicable for decreasing particle-size frac- tions and densities. Many highway and urban runoff particulates can have densities much less than sand. For example, tire particulates can have densities ranging from 1.02 to 1.36 g/cm3, and asphalt particulates can have densities ranging from about 1.1 to 1.5 g/cm3 (Butler et al. 1996, Edil and Bosscher 1994, Lide 1997, Li et al. 2006, Lin 2003). The following considerations are critical when considering structural BMP implementation for sediment removal: • Pretreatment: Sediment removal is most effective when pretreatment structures are employed to remove coarse sediment fractions. This improves the efficiency of downstream practices by reducing clogging risk and the frequency of required maintenance. Applicable pretreat- ment devices include screening equipment, vaults, sumps, filter strips, grassed swales, and sedimentation forebays. • Treatment train design: When designing passive sediment removal systems (i.e., systems that do not rely on external energy sources to accomplish treatment), designers should consider a progression from coarse to fine sediment removal in successive treatment components. Filtra- tion should occur after screening and sedimentation treatment processes have been employed. Pollutant Name Size Description Primary Roadway Source Applicable Treatment Processes Gross Solids Diameter ≥ 5 mm Large particles, mostly transported as bed load or as floatable load. Trash, organic debris, and coarse particles Screening, separation Settleable Solids Diameter ≥ 20 µm Suspended sediments that can be rapidly removed from the water column by sedimentation. Soil particles, road sand, pavement wear Sedimentation, separation Fine Solids Diameter < 20 µm Small suspended particles, including dissolved and colloidal fractions. Atmospheric deposition and vehicle emissions Filtration, coagulation– flocculation Table 24. Primary sediment constituents found in roadway runoff.

Compliance Strategies Approach 53 • Maintenance access: To maintain the function of structural practices, sediment removal and practice rehabilitation are required over time. System design should consider available space and how maintenance personnel and equipment can safely access the site, as well as sediment disposal requirements. Applicable removal strategies are dependent on the target sediment-size fraction, as described in the following sections. When multiple-size fractions are of concern, the treatment train design can be used to progressively remove large to small fractions. Removal of particles by filtration is dependent on the particle size and pore space of the filter media. Smaller filter media pore sizes improve the capture of small particles but at decreasing flow rates. Design flow rates and upstream ponding requirements are dependent on the head loss through the filter media. Over time, the required head loss increases due to clogging of the filter media and should be anticipated in initial design and specified maintenance protocols. Clogging rates depend on the filter media specifications and unit area sediment loading rate (Urbonas 1999, Avila et al. 2010). Pretreatment should be done before all filtration practices to reduce the sediment load on the filter media. Gross Solids (> 5 mm) Applicable Treatment Processes: Screening, separation. Gross solid pollutant loads from roadways are affected by location, land use, and season. Depending on the accumulated load, gross solids may be a substantial contributor of sediment and associated contaminants (Hunt et al. 2015). Applicable source control practices for gross solids include street sweeping or catch- basin cleaning and vegetation management plans that keep debris off the roadways. Gross solids can be separated from stormwater runoff by screening or separation operations using pretreat- ment devices, including solids removal devices or designed forebays. Settleable Solids (≥ 20 µm) Applicable Treatment Processes: Sedimentation, filtration. Settleable solids composed of inorganic particles greater than 20 µm are effectively removed from the water column by Source Cause State DOT Controllable Vehicle Use The abrasion of vehicle components (brakes and tires), undercarriage washing, and residues from combustion result in the buildup of fine solids on the road surface. No. It is a function of vehicle traffic volumes. Traction Sand Application The application of sand or other components to reduce skid hazards results in washoff of applied solids from the road surface. Yes. Application rates, timing, and compound type are adjustable. Wind and Erosion Deposition Air currents deposit fine particles on the road surface from nearby sources, such as industrial, agricultural, and exposed vacant land areas. No. It is a function of weather patterns and adjacent land uses. Plant Material Leaves and other plant materials that fall or are transported to the road surface as a function of season, landscaping, and management practices. Partially. Vegetation management plans can reduce buildup on road surface. Litter Refuse items discarded after human use. Partially. Litter ordinances, education plan, and removal plans may reduce litter volumes. Runoff from Adjacent Land and Stockpiles Runoff containing particulate matter from erosion of adjacent land—especially areas with exposed soil—can run onto the roadway or combine with drainage pathways. Partially. Function of topography, soil type, land ownership, and cover conditions. Areas with exposed soil can be remedied. Channel Erosion Drainage pathways from the right-of-way to the receiving water—including drainage ditches and outfalls—can contribute sediment via erosion and mass wasting. Partially. Areas susceptible to erosion can be identified and erosion protection implemented. Table 25. Controllability of primary sources of sediment in the highway environment.

54 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff gravitational sedimentation. Settleable stormwater solids typically have specific gravities between 1.5 and 3.0 (Li et al. 2006). Removal of settleable solids is a function of density, particle size, shape, and the hydraulic residence time within the practice. The sedimentation process can be estimated by particle settling theory to approximate the time for a particle of a specific size, density, and shape to settle from solution (Jiménez and Madsen 2003, Wu and Wang 2006). However, actual settling rates are confounded by turbulence and changes in temperature that affect the dynamic viscosity and density of water. Effective practices for sedimentation include catch-basin sumps, water quality swales, filter strips, and detention facilities (Avila et al. 2010, Stagge et al. 2012). Sedimentation ponds can be highly effective at removing suspended solids from stormwater runoff via sedimentation. Important design considerations include the potential for short-circuiting and resuspension of particles from the facility bottom, which can occur if the overlying water depth is not sufficient. Permanent pool depths greater than 1 foot can reduce particle resus- pension in ponds (Clark and Pitt 2012). Where space or detention time are not sufficient for settling, filters may be appropriate. PFC pavement has been shown to reduce suspended solids concentrations in roadway runoff by as much as a factor of 10 as compared to traditional pave- ment (Stanard et al. 2007). Fine Solids (< 20 µm) Applicable Treatment Processes: Filtration, coagulation–flocculation. Removal of sus- pended inorganic particles less than 20 µm generally requires coagulation–flocculation or filtration processes. Sedimentation basins can be enhanced to provide fine solid removal by employing inclined plate settlers or coagulation–flocculation. Inclined plate settlers are overlap- ping angled plates that increase the sedimentation surface area and reduce the distance particles must fall (Pitt et al. 1999). Coagulants destabilize colloids by reducing repulsive forces allowing larger particles—such as flocs—to form, which then settle from the water column. The use of coagulants requires an application method and has been used sparingly in stormwater treatment (Avila et al. 2010). However, situations requiring specific treatment objectives have successfully employed coagulation methods to improve removal efficiencies (Kim and Sansalone 2008). Removal of particles by filtration is dependent on the particle size and pore space of the filter media. However, smaller filter media pore sizes improve the capture of small particles at decreas- ing flow rates. Design flow rates and upstream ponding requirements are dependent on the head loss through the filter media. Over time, the required head loss increases due to clogging of the filter media and should be anticipated in initial design and specified maintenance protocols. Clog- ging rates are dependent on the filter media specifications and unit area sediment loading rate (Urbonas 1999, Avila et al. 2010). PFC pavement is also applicable to fine solids removal. Pretreat- ment should be done before all filtration practices to reduce the sediment load on the filter media. When selecting between possible sediment compliance strategies, various applicability factors, considerations, and constraints should be kept in mind, as summarized in Table 26. Nutrient TMDL Control Strategies Properties. Nutrients can be transported in both dissolved and particulate forms with runoff characteristics determined by the pollutant’s solubility properties. Nitrogen is pre- dominantly dissolved in roadway runoff. If nitrogen accumulates, it dissolves into soluble forms during rainfall events (Miguntanna et al. 2013). Phosphorus, however, is predominantly particulate-bound and mobilized when it is attached to sediment (Helmreich et al. 2010). High-intensity events can increase phosphorus runoff concentrations due to the mobilization of larger particles (Miguntanna et al. 2013). Particulate-bound pollutants can be removed by physical processes, such as filtration and sedimentation. But dissolved constituents are harder to

Compliance Strategies Approach 55 Compliance Strategy Method Components Applicability Critical Considerations Critical Constraints Traction Control Plan Source control Reduce sand application rate or switch to alternative material Cold weather climate in which road sanding has been identified as a contributor to sediment loading Identify methodology and consequences of implementing change to traction material application • Public safety • Institutional coordination • Equipment availability • Maintenance • Accessibility • Cost Erosion Control Source control Vegetation or material coverage of exposed soil, channel banks, or outfalls Construction sites or bare areas in state DOT jurisdiction Erodible landscapes or flow paths identified in the watershed Identify applicable erosion control practices and areas for implementation • Longevity • Maintenance • Accessibility • Cost Street Sweeping/ Catch-Basin Cleaning Source control Routine removal of solids from road surface or catch-basin sumps using a Vactor truck or sweeper truck Solids-size fraction of concern has been identified and is removable using prescribed methods Identify anticipated frequency and removal method to achieve pollutant load reduction • Institutional coordination • Equipment availability • Operational costs • Material disposal • Maintenance • Accessibility • Cost Infiltration Volume reduction Basins, vaults, trenches, underground injection controls, or dispersion Applicable to all situations if constraints met Identify available space and moderate to high permeability soils • Soil- infiltration capacity • Groundwater contamination • Space • Clogging • Maintenance • Accessibility • Cost Detention Flow attenuation, separation Detention ponds, wet ponds, or wetlands Solids-size fraction of concern is settleable (≥20 µm) Inclined plate settlers or coagulation– flocculation enhancements for fine solids-size fractions (<20 µm) Identify available space and settleable fraction based on particle settling theory • Space • Maintenance • Accessibility • Cost Filtration Filtration/ sorption Bioretention, media filters, or PFC pavement Solids-size fraction of concern is fine (<20 µm) or settleable (≥20 µm) Identify available space and filter media parameters and construction schedule for replacement of road surfaces with PFC pavement • Space • Clogging • Maintenance • Accessibility • Cost Table 26. Sediment compliance strategies.

56 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff remove, requiring sorption or biological mechanisms. The difference in chemical characteristics of dissolved nutrients—including charge and oxidation state—has significant implications for selecting compliance strategies (Table 27). Sources. The sources of nutrients in roadway runoff include both natural sources—such as soils and vegetation—and anthropogenic sources, such as runoff from agricultural practices. Some sources can be controlled, while other sources are more difficult or impossible to actively manage (Table 28). For those sources that are at least partially controllable, source control prac- tices may prove to be important in reducing nutrient loads. Treatability. The primary considerations for particulate-bound nutrients are the same as those for sediment control, including pretreatment, treatment train design, and maintenance access (see Sediment TMDL Control section). Strategies for dissolved nutrient removal are dependent on the type and chemical nature of the nutrient of concern (Table 29). The following considerations are critical when taking into account BMP implementation for dissolved nutri- ent removal: 1. Anoxic designs: Dissolved nitrogen removal is most effectively managed in the presence of both an aerobic and an anoxic zone. Within aerobic zones, nitrifying bacteria transform am- monia to nitrite and nitrate, and within anoxic zones denitrifying bacteria transform nitrate to nitrogen gas. Without a maintained anoxic zone, the system leaches nitrate and nitrite, both from influent loading and from TKN that has been aerobically transformed to nitrate or nitrite. Anoxic zones can be created in filtration BMPs by forcing a layer of saturation using an elevated underdrain or an upturned elbow at the outlet control structure to promote denitrification (Brown and Hunt 2011). 2. Media amendments: To bind dissolved phosphorus in a more efficient and irreversible manner, media amendments such as iron, fly ash, or water treatment residual can be added to biofilters. Media amendments such as peat, coconut coir, expanded clay, tire crumb, wood fibers, biochar, activated carbon, and other materials may also promote the conditions neces- sary (e.g., low oxygen, electron donor, and moisture) to remove nitrogen through biosorption processes (Wanielista et al. 2017). Designed media composed of several media amendments can be used to specifically target an array of POCs. Fully aerobic systems with organic- amended media are not suggested, as decay of organic material releases additional nutrients (Bratieres et al. 2008). Pollutant Name Description Primary Roadway Source Applicable Treatment Processes Nitrogen: Total All forms of nitrogen, including particulate and dissolved forms Organic debris, soil particles, fertilizers, deposition Sedimentation, filtration, and coagulation– flocculation Nitrogen: TKN Nitrogen in the form of organic-N (both particulate and dissolved) and ammonia-N Fertilizers, organic debris, animal and human waste Sorption, ion exchange, microbial transformation, and uptake and storage Nitrogen: Nitrate/Nitrite Dissolved, oxidized forms of nitrogen Fertilizers, rainfall Microbial transformation and uptake and storage Phosphorus: Total All forms of phosphorus, including particulate and dissolved Organic debris, soil particles, fertilizers, deposition Sedimentation, filtration, and coagulation– flocculation Phosphorus: Dissolved Dissolved forms of phosphorus, including organic-P and ortho-P, and soluble reactive phosphorus Fertilizers, organic debris, animal and human waste, detergents Sorption, ion exchange, and uptake and storage Table 27. Primary nutrient constituents found in roadway runoff.

Compliance Strategies Approach 57 Source Cause State DOT Controllable Dry Deposition Air currents deposit fine particles on the road surface from nearby sources, such as industrial, agricultural, and exposed vacant land areas. These particles can have particulate nutrients associated with them. No. It depends on weather patterns and adjacent land uses. Plant Material Leaves and other plant materials fall or are transported to the road surface due to changes in the season, landscaping, and management practices. Partially. Vegetation management plans can reduce accumulation on the road surface. Runoff from Adjacent Land Runoff containing particulate matter from erosion of adjacent land, especially areas with exposed soil, can run onto the roadway or combine with drainage pathways. Adjacent farmland that has been fertilized can also contribute heavily to dissolved nutrient loads. Partially. It depends on topography, soil type, land ownership, and the condition of vegetation. Areas with exposed soil can be remedied. Regulations regarding fertilizer application, frequency, and type could prevent inputs. Channel Erosion Drainage pathways from the right-of-way to the receiving water, including drainage ditches and outfalls, can contribute particulate-bound nutrients via erosion and mass wasting. Partially. Areas susceptible to erosion can be identified and erosion protection implemented. In addition, it also depends on land ownership. Vehicle Use Vehicle exhaust contains nitrates, and some vehicle lubricants and other auto-related chemicals contain phosphates. No. It depends on vehicle traffic volumes. Fertilizer Use State DOTs sometimes use fertilizers in hydroseed applications and to maintain vegetation in medians and on areas adjacent to roadways but still within the state DOT right- of-way. Yes. Alternative fertilizers, such as slow-release fertilizers, could be used. Fertilizer use could be restricted. Table 28. Controllability of primary sources of nutrients in the highway environment. 3. Plants: Vegetation absorbs and stores nutrients during growth periods. System design should account for regular removal of plants to prevent decay and subsequent re-release of nutrients. The applicable removal strategies depend on the targeted nutrient form, as described below. When multiple forms and types of nutrients are of concern, a multistage system can be used (with the bottom layer subjected to anoxic conditions). Table 29 is a summary of the possible nutrient compliance strategies that should be evaluated. Nitrogen: Total Applicable Treatment Processes: Sedimentation, filtration, coagulation–flocculation. TN loads can be reduced by removing particulate nitrogen. The applicable source control practices are similar to those used for solids removal, especially vegetation management since organic material tends to be high in nitrogen. Treatment systems that physically remove solids—such as sedimentation, filtration, and coagulation–flocculation—are effective at removing particulate nitrogen. Nitrogen: TKN Applicable Treatment Processes: Sorption, ion exchange, microbially mediated transfor- mations, uptake and storage. Limited sorption of ammonia-N can be achieved through adsorption to biofiltration media with a high cation exchange capacity (Dietz 2007). However, reduction of TKN loads is generally achieved through microbially mediated transformation to nitrate and nitrite by the process of nitrification, which occurs naturally under aerobic condi- tions. The main constraint for this process is to ensure a sufficiently long aerobic period for transformation to occur. PFC pavement has been shown to reduce TKN concentrations, as well (Stanard et al. 2007). Vegetative uptake and storage can also assist in the treatment of TKN in

58 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff Compliance Strategy Method Components Applicability Critical Considerations Critical Constraints Vegetation Management Source control Removal of leaves and mowing of overgrown vegetation to prevent decay and nutrient release Areas with high concentrations of trees, vegetated medians, or shoulders Identify locations of concern, frequency, and timing of maintenance • Equipment availability • Institutional coordination • Maintenance • Accessibility • Cost Erosion Control Source control Vegetation or material coverage of exposed soil, channel banks, or outfalls Erodible landscapes or flow paths have been identified in the watershed Identify applicable erosion control practices and areas for implementation • Longevity • Plant establishment • Maintenance • Accessibility • Cost Infiltration Volume reduction Basins, vaults, trenches, or dispersion Applicable to all situations if constraints are met Identify available space and soils with moderate to high permeability • Soil- infiltration capacity • Groundwater contamination • Space • Clogging • Geotechnical stability • Maintenance • Accessibility • Cost Detention Flow attenuation, separation Detention ponds, wet ponds, or wetlands Particulate nutrients are associated with settleable solids (>20 µm) Identify available space and determine if settleable fraction is large enough to be useful in reducing nutrient loads • Space • Maintenance • Accessibility • Cost Filtration Filtration/ sorption Bioretention filters, filter amendments Particulate nutrients and possibly dissolved phosphorus or TKN are of concern Identify available space and filter media parameters • Space • Clogging • Maintenance • Accessibility • Cost Multistage Filtration with Anaerobic Zone Microbially mediated transformation Bioretention filters with saturated zone, electron donor material Particular concern for dissolved nitrogen, especially nitrate and nitrite Identify available space, filter media parameters, potential for anoxic zone • Space • Clogging • Maintenance • Accessibility • Cost Vegetated Conveyance Uptake and storage Vegetated swale or filter strip with or without amended soils Dissolved nutrients, areas where plants are not dormant during wet season Identify available space and maintenance plan for vegetation harvesting • Space • Clogging • Maintenance • Accessibility • Cost PFC Pavement Filtration/ sorption PFC-paved roadways TKN, nitrate Identify feasibility of pavement replacement maintenance plan and life span needs. • Clogging • Maintenance • Longevity • Timing • Accessibility • Cost Table 29. Nutrient compliance strategies.

Compliance Strategies Approach 59 runoff. Vegetated columns improved ammonia removal in gravel and sand mesocosms when comparing vegetated to unvegetated columns (Henderson et al. 2007). It is important that flows in vegetated areas be slow enough to allow for vegetative uptake and storage to occur and that removal not occur during periods when plants are dormant. Nitrogen: Nitrate/Nitrite Applicable Treatment Processes: Microbially mediated transformations, uptake and storage. Nitrate and nitrite do not readily sorb to typical biofiltration media (LeFevre et al. 2014). One way to reduce nitrate and nitrite loading is through the microbially mediated trans- formation known as denitrification. This process occurs naturally but only in the absence of oxygen. An anaerobic zone can be created in a biofilter by maintaining a saturated zone and adding a carbon source to serve as an electron donor. This method has been successfully applied at a pilot scale using an upturned elbow pipe and adding newspaper media (Kim et al. 2003). Another major mechanism for nitrate and nitrite reduction is vegetative absorption. In a study that compared vegetated and nonvegetated sandy loam mesocosms, vegetated systems removed 79 percent to 93 percent of nitrate input loads; nonvegetated systems did not remove any of the influent nitrate load (Henderson et al. 2007). Therefore, the flow rate and plant growth periods are critical design parameters for nutrient removal by vegetation. PFC pavement has shown some capability for reductions in nitrate concentrations from high- way runoff (Stanard et al. 2007). Phosphorus: Total Applicable Treatment Processes: Sedimentation, filtration, coagulation–flocculation. In road runoff, a high percentage of phosphorus usually exists as particulate phosphorus. So, TP loads can be greatly reduced by removing particulate phosphorus. Studies have shown that removing the settleable solids fraction reduces TP by about two-thirds, and removing both fine and settleable solids can reduce TP by more than 90 percent (Clark and Pitt 2012). The applicable source control practices are similar to those used for solids removal, with particular consider- ation for vegetation management since organic material tends to be high in phosphorus con- tent. Treatment systems—such as sedimentation, filtration, and coagulation–flocculation—that physically remove solids are effective in removing particulate phosphorus. Phosphorus: Dissolved Applicable Treatment Processes: Sorption, ion exchange, uptake and storage. Dissolved phosphorus does not readily sorb to sand. But by amending sand with a material that is more reactive to phosphorus, a filter’s capacity for phosphorus removal can be greatly improved. Some amendments that have produced favorable results include iron filings, which captured 88 percent phosphate in a sand filter amended with 5 percent iron filings (Erickson et al. 2012); fly ash, which captured 85 percent of phosphorus mass in a sand column amended with 5 percent fly ash (Zhang et al. 2008); and water treatment residual, which reduced phosphorus mass loadings from 95 percent to 99 percent (Lucas and Greenway 2011). If iron filings are used, aerobic con- ditions should be maintained to avoid iron oxidation and subsequent leaching, resulting in the release of sorbed phosphates. Vegetative uptake can also be applied to systems where removing dissolved phosphorus is required. The presence of vegetation has been shown to improve ortho- phosphate removal when comparing vegetated to unvegetated columns (Henderson et al. 2007). Metals TMDL Control Strategies Properties. Metals in roadway runoff can be categorized as either a particulate-bound form or a dissolved fraction form (Sansalone and Buchberger 1997). Metal types in highway runoff typically include iron, copper, lead, cadmium, nickel, and zinc (Barrett et al. 1995A). Particulate- bound metals have a high affinity for adhering to fine sediment, such as particles from tires,

60 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff brake parts, and road surfaces. The fraction-form metals not bound to particulates exist in a dis- solved state as free metal ions, as inorganic complexes, or bound to dissolved organic chemicals. The important factors that lead to high concentrations of metals within the water body include traffic volume, rainfall patterns, antecedent dry period, and storm intensity and dura- tion (Kearfott et al. 2005). Studies have shown that high concentrations of zinc and copper are correlated to TSS concentrations (Washington State Department of Transportation 2007). Additionally, when both dissolved-form and particulate-bound metals are analyzed, a major- ity of total metals are found to be associated with particles (Washington State Department of Transportation 2007). The difference in chemical characteristics of metals is critical to selecting compliance strategies (Table 30). Sources. The sources of metals in roadway runoff—as identified by Folkeson (1994)— include vehicular traffic, litter, spills, and roadway maintenance operations (Kearfott et al. 2005). Specifically, metals are generated from friction in the engine and suspension system, brake pad and tire wear, rust and corrosion, plated traffic railings, pavement abrasions, and deicing salts (Kearfott et al. 2005). Table 31 presents the primary sources of metals and the practicality of controlling the discharge of those metals from that source. Due to the correlation between met- als and sediment, the factors (including control strategies) considered for suspended solids— specifically, fine sediment—are applicable to metals, as well. Another source of metals from highways is atmospheric deposition, which can significantly impact pollutant loads (especially for suspended solids, metals, and nutrients) (Barrett et al.1995B). In addition, hazardous air pollutants released from coal-fired power plants directly release pollutants—such as cadmium, nickel, selenium, and lead, among other types of metals. Pollutant Name Description Primary Roadway Source Applicable Treatment Processes Cadmium Dissolved and total cadmium Soil particles, fertilizers, galvanized culverts and guardrails Sedimentation, filtration, source control, sorption, biological uptake, coagulation– flocculation Copper Dissolved and total copper Soil particles, brake pads Lead Dissolved and total lead Soil particles, tires, brake pads, lead weights Nickel Dissolved and total nickel Soil particles, vehicle engines Zinc Dissolved and total zinc Soil particles, brake pads, tires, galvanized culverts and guardrails Table 30. Primary metals constituents found in roadway runoff. Source Cause State DOT Controllable Vehicular Traffic The abrasion of vehicle components (brakes and tires) and residues from combustion result in the buildup of fine metals on the road surface that are bound to suspended solids. No. Dependent on vehicle traffic volumes Litter Refuse items discarded after human use Partially. Litter ordinances, education plans, and removal plans may reduce litter volumes. Slope Erosion Rainfall drainage from highways contains sediment contaminated with particulate-bound metals from vehicular traffic. Partially. Susceptible areas can be identified, and source control measures can be implemented. Roadway Maintenance Activities Runoff containing particles from areas where active construction or road repairs are occurring can contribute to heavy metal loads. Deicing salt activities can increase the salinity and transport of some metals in snowbank meltwater. Partially. Susceptible areas can be identified, and source control measures can be implemented. Implement quantity control of deicers. Table 31. Controllability of primary sources of metals in the highway environment.

Compliance Strategies Approach 61 Treatability. Runoff characterizations have indicated that the concentration of metals in highway runoff is often correlated to TSS. Therefore, the appropriate control measures for met- als are controlling erosion and preventing or minimizing the discharge of fine sediment. This can be achieved for particulate-bound metals through the implementation of sediment con- trols, including pretreatment and treatment train design (see Sediment TMDL Control sec- tion). The UTPs of sedimentation, filtration, and sorption are suitable for reducing metal loads to the receiving water body. Also suitable are efforts to use alternate coal in power plants that directly harm the atmosphere and increase deposition of various metals. Several ongoing alter- native treatability include reducing copper in brake pads, reducing the size of wheel weights, and changing the formula of tires. Particulate-Bound Metals. A study conducted by the Texas Department of Transporta- tion determined that lead was correlated to solids (sediment) at a 99 percent confidence limit at the six monitored sites (Barrett et al. 1993). Of the six sites evaluated, all had a correlation between zinc and cadmium to sediment, while five sites showed a correlation between copper with sediment (Barrett et al. 1993). Therefore, it can be deduced that particulate cadmium, copper, lead, nickel, and zinc loads can be reduced through effective source control practices that are similar to those identified for sediment removal. The primary and most effective control measures for particulates are those that settle or filter the particulates within the highway runoff (Barrett et al. 1993). This can be attained through the implementation of pretreatment devices to various structural controls, such as infiltration basins or trenches and media filters. Reducing particulate-bound metals can also be effectively achieved by intercepting and filtering runoff, avoiding excess flows in natural channels and drains, and maintaining runoff flow patterns. Particulate discharge from the roadway may also be controlled by a PFC overlay. Additionally, infiltration systems can be implemented to treat surface runoff prior to discharge into the water body. The removal efficiency for trace metals through infiltration practices has been shown to achieve approximately 90 percent effectiveness (Barrett et al. 1993). Additionally, Schueler et al. (1992) showed that maintained and adequately designed grassed swales may remove up to 70 percent of TSS and between 50 percent and 90 percent of various metals. Dissolved Fraction Metals. The size of the metal particles determines their capability to settle in appropriate treatment devices. The removal of particulate metals may also reduce the concentration of dissolved fraction metals; however, additional control measures are necessary. The treatment of dissolved fraction metals requires physical structures that prevent contami- nated runoff from reaching receiving waters. These structures can consist of infiltration systems that allow roadway runoff to percolate into the soil or through filter media where adsorption can occur. NCHRP Report 767 identified treatment approaches—such as infiltration systems (e.g., infiltration basins or trenches) and biofiltration systems (e.g., vegetated buffer strips and swales)—that are effective in reducing dissolved constituents (Barrett et al. 2014). Additionally, NCHRP Report 767 also indicated that adsorption or engineered media is an effective methodol- ogy in removing dissolved metals from the roadway runoff (Barrett et al. 2014). Several effective engineering media types—including sand, gravel, perlite, bricks, and organic media—can be used for transferring the dissolved metal mass (Barrett et al. 2014). Table 32 summarizes the metal compliance strategies and the constraints that should be considered when evaluating these strategies. Bacteria TMDL Control Strategies Bacteria are present in the surface water as either unattached or adsorbed to the sediment. The presence of waterborne pathogens is identified by monitoring the quantity of indicator bacteria (fecal coliform, E. coli, total coliform, and enterococcus). The indicator bacteria are associ- ated with warm-blooded animals and are generally rare or absent in unpolluted waters. Many

62 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff Compliance Strategy Method Components Applicability Critical Considerations Critical Constraints Street Sweeping/ Catch-Basin Cleaning Source control Routine solids removal from road surface or catch- basin sumps using a Vactor truck TSS are a concern for metals and are removable using prescribed methods. Identify anticipated frequency and removal method to achieve pollutant load reduction. • Institutional coordination • Equipment availability • Operational costs • Material disposal • Maintenance • Accessibility • Cost Pretreatment Structure (sedimentation basin) Source control Basins or vaults Applicable to all situations if constraints are met Identify available space. • Soil infiltration capacity • Groundwater contamination • Space • Longevity • Capacity • Maintenance • Accessibility • Cost Infiltration Volume reduction Basins, vaults, trenches, underground injection controls, or dispersion Applicable to all situations if constraints are met Identify available space and moderate-to-high permeability soils. • Soil infiltration capacity • Groundwater contamination • Space • Clogging • Maintenance • Accessibility • Cost Filtration Filtration/ sorption Bioretention filters, filter amendments Particulate metals and dissolved metals are of concern. Identify available space and filter media parameters. • Space • Clogging • Maintenance • Accessibility • Media replacement • Accessibility • Cost Vegetated Conveyance (biofiltration strips and swales) Uptake and storage Vegetated swale or filter strip, with or without amended soils Dissolved metals and total metals are of concern. Identify available space and maintenance plan for vegetation harvesting. • Space • Clogging • Maintenance • Accessibility • Cost Reducing Galvanized Structures Source control Guardrails, fences, sign posts, or pipes Particulate zinc, particulate cadmium, dissolved zinc, and dissolved cadmium are of concern. Identify locations with galvanized downspouts and paint/coat (containing no zinc) these structures. • Longevity • Maintenance • Accessibility • Cost PFC Pavement Filtration/ sorption PFC-paved roadways Particulate metals and dissolved metals Identify feasibility of pavement replacement, maintenance plan, and life- span needs. • Clogging • Maintenance • Longevity • Timing • Accessibility • Cost Table 32. Metal compliance strategies.

Compliance Strategies Approach 63 waterborne diseases, such as dysentery and cholera, are associated with certain strains of E. coli. Because of the serious potential health threat associated with certain strains of this general type of bacteria, their presence is a very important indicator of the health risk associated with human contact with a body of water. Bacteria TMDLs often include requirements for dry weather flows and wet weather flows. Dry weather nonstormwater discharges may significantly increase bacteria loading to receiving waters. State DOTs generally do not generate nonstormwater discharges, but such discharges may be present in department systems from high groundwater or upstream sources. Additional bacteria sources include illicit discharges and seepage from failing septic systems or concentrated animal feeding operations. However, bacteria TMDLs generally include a dry weather TMDL component requiring control measures to be implemented. Therefore, bacteria TMDL control strategies may include dry weather monitoring programs. The reduction of nonstormwater dis- charges can be achieved through infiltration, diversion, enforcement against illicit discharges, or other methods. Wet weather stormwater discharges also contribute significant bacteria loads to receiving waters. The principal impact is to the water contact recreation beneficial use and drinking water. State DOTs implement control measures and BMPs to prevent or eliminate the discharge of bac- teria from their right-of-way. Source control and preemptive activities—such as street sweep- ing, clean-up of illegal dumping and unauthorized encampments, public education on littering, and BMPs such as retention–detention, infiltration, and diversion of stormwater—reduce the discharge of bacteria to receiving waters. State DOTs are unlikely to be primary contributors of bacteria and viruses responsible for human health threats. However, state DOTs are listed as stakeholders within these TMDLs due to the presence of bacteria within the storm drain net- work. Alternative approaches to compliance may consist of watershed management through a regional BMP and other cooperative implementation. Properties. Many factors affect the general fate of bacteria and, in particular, fecal coliform. These factors can be divided into physical, physicochemical, biochemical, and biological factors. The bacterial die-off follows a first-order decay equation. Some of the factors that affect the die-off rate of bacteria include temperature, sedimentation, pH, nutrient level, and presence of organic substance. Temperature is the most important factor affecting the fate of bacteria. The range of the optimal or detrimental temperatures for survival and die-off varies for specific types of bacteria. Sedimentation may decrease the mortality rate by depositing the bacteria to the bottom of the stream bed. In addition, an increase in nutrient level and organic substance may also increase the amount of in-stream fecal coliform and decrease the mortality rate. Typically, E. coli survives longer in lower pH. The effective UTPs of reducing bacteria from the watershed include hydrologic operation, physical treatment, and chemical processes. These UTPs consist of sorption and filtration, as identified in Table 33. Sources. Humans and animals are the primary sources of pathogenic bacteria. Most of the pathogens found in surface water are excreted with fecal matter from animals or humans. These organisms enter surface water through contamination by human fecal waste and sewage or from animal fecal waste. Indicator bacteria such as E. coli are present in high numbers in human and animal waste. Potential pathogen sources can be either point sources or nonpoint sources. Major point sources of pathogens are the discharges from wastewater treatment plants; combined sewer overflows; concentrated animal feeding operations; slaughterhouses and meat processing facili- ties; tanning, textile, and pulp and paper factories; and fish and shellfish processing facilities (EPA 2001). Nonpoint sources of pathogens include urban litter; contaminated refuse; domestic pet and wildlife excrement; failing septic systems; failing sewer lines in urban and suburban areas and concentrated animal operations; excrement from barnyards, pastures, rangelands, and

64 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff feedlots; and uncontrolled manure storage areas in rural or agricultural areas. The point sources tend to have the most profound influence on receiving water bodies during dry conditions. Similarly, nonpoint sources like runoff from urban and agricultural areas cause the most effects during a storm event. Typical state DOT sources within the highway environment include RVs, septic-waste transport trucks, waste trucks, animal transport trucks, storm drains, wildlife, and unauthorized encampments. Nonpoint sources are those that originate over a more widespread area and can be more dif- ficult to trace back to a definite starting point. Failed on-site wastewater disposal systems (septic systems) in residential or rural areas can contribute high quantities of coliforms and other bac- teria to surface water and groundwater. Other contributors of increased levels of bacteria being discharged from the highway environment may consist of run-on from adjacent land uses. Land uses that may have had failing septic systems or high levels of animal waste lead to higher con- centrations of bacteria being discharged onto a state DOT right-of-way. Run-on from adjacent land uses can also contribute heavily to the bacteria impairment downstream. Addressing failing septic systems is outside state DOT purview, but departments could identify and characterize seeps and other points of right-of-way onflow with high bacteria concentrations and share the information with appropriate agencies responsible for permitting and regulating such systems. Other solutions may include physical separation, which may include diversion structures and parallel conveyances to avoid comingling of highway runoff with off-site flows. Table 34 identifies the potential sources of bacterial contamination, their cause, and whether they are controllable. Treatability. The treatment mechanisms applicable to bacteria include infiltration, ultra- violet treatment, detention, and source control. The UTPs of sorption and filtration are suitable for decreasing bacteria from the water column. When structural controls are deemed infeasible, however, any approach to reduce bacteria in the watershed should include options to reduce bacteria at their source. Source control may be less costly and more reliable than the outfall-based approach while still attaining the WLAs. Source controls address the illicit or accidental discharges of human waste, as well as control or eliminate the wildlife and pets associated with pathogenic bacteria in the watershed. Some of these measures may not be a state DOT’s responsibility; how- ever, collaborating with the communities or stakeholders may reduce the burden on state DOTs. As shown in Figure 21, the applicable removal strategies are dependent on the target size fraction. The range of the particle size varies between 0.25 µm and 1 µm for all primary bacteria Pollutant Name Size Description Roadway and Run- On–Runoff Sources Applicable Treatment Processes Total Coliform Diameter ≥0.5 µm Bacteria commonly found within soil or vegetation, which are typically harmless Human/animal/wildlife/ livestock waste, septic systems, CAFOs, roadkill Sorption, filtration Fecal Coliform Diameter ≥0.5 µm Bacteria commonly found within intestines of humans and warm-blooded animals Animal/wildlife/livestock waste, CAFOs, roadkill E. coli Diameter = 0.25 µm – 1 µm Subgroup of fecal coliform that is a type of bacteria found within intestines of warm- blooded animals and may include human pathogenic strains Unauthorized encampments, recreation users, human/livestock waste, leaking septic systems, roadkill Enterococcus Diameter = 0.5 µm – 1 µm Bacteria commonly found within intestines of humans and warm-blooded animals Recreation users (swimming, tubing, fishing, boating, and aesthetic use), roadkill Note: CAFO = concentrated animal feeding operation. Table 33. Primary bacteria constituents found in roadway runoff.

Compliance Strategies Approach 65 strategies identified within Table 35. Therefore, they require similar treatment processes. Table 35 presents a list of compliance strategies for various types of bacteria and the factors to consider prior to selection and implementation. Chloride TMDL Control Strategies Properties. Roadways in cold climates are susceptible to increased chloride loading due to deicing applications. For example, the estimated chloride concentrations from instantaneous specific conductance measurements at a USGS monitoring station near Littleton, Massachusetts, resulted in measurements ranging between 0.11 and 26,500 mg per liter between October 1, 2005, and September 30, 2007 (Granato et al. 2015). Chloride is highly soluble in water. Once it enters a water body, it generally exists in the dis- solved form and does not react with most solutes and sediments found in water (Granato et al. 2015). As such, chloride is highly mobile in runoff, surface water, and groundwater. Sources. Chloride in runoff is mainly caused by anthropogenic activities, particularly the application of deicing chemicals for traction control. Fertilizers and animal waste can have measurable effects on chloride loads in some areas (Granato et al. 2015). Although some Source Cause State DOT Controllable Illicit Discharge Illicit connections to storm sewers are a source of bacteria in surface waters, even during dry periods. A connection to a storm sewer is "illicit" when the wastewater requires treatment prior to discharge and should be routed to the sanitary sewer. Only stormwater and certain permitted discharges (e.g., clear, noncontact, cooling water) should be discharged to a storm sewer. According to federal regulations, any discharge to an MS4 that is not composed entirely of stormwater is an illicit discharge. Illicit discharges enter the system through either direct connection (e.g., wastewater piping mistakenly or deliberately connected to the storm drains) or indirect connections (e.g., infiltration into the MS4 from cracked sanitary systems, spills collected by drain outlets, or paint or used oil dumped directly into a drain). The illicit discharges that contribute pathogens include sanitary wastewater and effluent from septic tanks. Yes. Through strict regulation measures, such as an illicit discharge detection and elimination program, septic system inspection programs (led by local regulators), or storm drain markers. Wildlife Population Typical species of wildlife that inhabit urban areas include deer, raccoons, muskrats, birds, bats, and beavers. Partially. Through vegetation management and installation of antiroosting nets and spikes under bridges to potentially reduce the areas of contamination. Livestock Livestock generally do not directly contribute bacteria to a state DOT’s right-of-way. Overland flow coming from agricultural land, the transport of livestock, and the track out from feedlots can contribute directly by transporting bacteria freely (dissolved) or within organic particles. Partially. Through vegetation management and source control measures to prevent run- on from adjacent land use; planting pond buffers and replacing turf with shrubs and trees potentially reduces areas of contamination. In addition, fencing can keep cows out of state DOT right-of-way or other stormwater treatment devices. Migratory Birds Landscaping practices may create ideal habitats for geese and other migratory waterfowl, concentrating populations during the nesting season or creating year-round flocks. Such habitats can create hazardous quantities of fecal litter, leaving E. coli and other disease-causing organisms ready to be washed into ponds and waterways. Partially. Planting pond buffers, replacing turf with shrubs and trees, and interfering with feeding and nesting potentially reduces areas of contamination. Domestic Pet Waste Pet waste that is improperly disposed of washes onto surface water bodies either directly or via storm drains. Partially. Through litter ordinances and public education and awareness plan. Table 34. Potential sources of bacterial contamination.

66 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff natural sources of chloride (such as atmospheric deposition) exist, these contributions tend to be significant only in coastal areas (Granato et al. 2015) (Table 36). Treatability and Other Considerations. Due to their solubility and mobility, chloride salts typically cannot be cost-effectively removed from stormwater. Energy-intensive, advanced treatment processes—such as flash evaporation or reverse osmosis—are required to achieve significant reductions. As such, source control is often the only viable alternative. In addition, chloride salts can alter the performance of structural BMPs in treating other contaminants (Kratky et al. 2017). The following are critical considerations when evaluating chloride control options: 1. Source control: Since removing chloride from water is difficult, source controls should be evaluated first. The ability to optimize timing and location of salt application could prove to be key. Alternative deicing chemicals, such as calcium magnesium acetate, should also be strongly considered. Compliance Strategy Method Components Applicability Critical Considerations Critical Constraints Infiltration Volume reduction Sand filter system or infiltration trenches Applicable to all situations if constraints are met Identify available space and filter media parameters. • Soil infiltration capacity • Groundwater contamination • Space • Clogging • Maintenance • Accessibility • Cost Filtration Filtration/sorption Bioretention or media filters Applicable to all situations if constraints are met Identify available space and filter media parameters. • Space • Clogging • Maintenance • Accessibility • Cost Retention Volume storage/filtration Retention pond, wetland basin Applicable to all situations if the runoff is completely contained in the system Identify available space. This practice may not be feasible within the right-of-way but may be feasible through partnerships with the local community. • Space • Soil media • Maintenance • Accessibility • Cost Inspection Source control Illicit discharge detection and elimination program, septic system inspection programs, storm drain and catch-basin marking Applicable to all situations if constraints are met Identify appropriate staff and frequency of inspection. • Resources (e.g., staff availability) • Maintenance • Accessibility • Cost Educational Source control RV waste disposal education and information, mass media campaign or public education program, pet waste education Applicable to all situations if constraints are met Identify the best media to maximize the effectiveness of the educational program. • Resources (e.g., staff availability) • Maintenance • Accessibility • Cost Natural Source control Landscaping practices (wildlife and bird netting or fencing) Applicable to all situations if constraints are met Partnership with other stakeholders • Resources (e.g., staff availability) • Maintenance • Accessibility • Cost Table 35. Bacteria compliance strategies.

Compliance Strategies Approach 67 2. Space availability: Some of the best options for dealing with chloride TMDLs may involve evaporation or retention. Therefore, available space may be critical in chloride treatment. 3. Vegetation type: When treating runoff from a road that is subject to high salt applications, it is important to select salt-tolerant vegetation. Although vegetation is unlikely to be the primary treatment method for chloride removal, selecting the right type of vegetation is critical if it is involved in the BMP design for aesthetics or for removal of a different type of contaminant. 4. Media type: Deicing salts can have a negative impact on structural BMPs due to the adsorp- tion of sodium by clay particles, causing dispersion and reducing infiltration rates (Kratky et al. 2017). BMPs with high sodium adsorption ratio soils are prone to clogging when deicing salts are applied to the roadway. Source Control Practices. The development of a salt management plan is critical to achiev- ing compliance with chloride TMDLs. It could include such topics as staff training, identifying salt-vulnerable areas, and evaluating salt storage sites (Fay et al. 2013). State DOTs may consider partnerships with other agencies to develop basin-wide deicing application reduction plans that include state and local jurisdictions, as these areas may account for substantial road miles (Stonewall et al. 2018). The application of dry salt can result in material loss due to bounce, traffic, and wind. One case showed that using prewetted material can reduce product use by 15 percent (Fay et al. 2013). Direct liquid application of materials has been shown to reduce application rates, improve the time to effect, and increase the accuracy of application (Peterson et al. 2010). Anti-icing practices—in which chemicals are applied prior to the formation of ice—also reduce the amount of chemicals needed to maintain road traction (Kahl 2002). In strategic locations, thermal deicing methods—such as the use of geothermal energy, electri- cally heated concrete, or special pavements that reduce the ability of ice to bind to the roadway surface—may be a viable alternative to the application of traction-control materials. These special pavements include those that incorporate flexible elements, such as rubber, and those treated with textured seal coats (Fay et al. 2013). Another important consideration is the use of nonchloride chemicals for deicing applications. A wide variety of alternatives are available. Acetates and formates (such as calcium magnesium acetate) are effective and tend to be less harsh than chloride salts, although they are more expen- sive and have a narrower effective temperature range than rock salt. Urea and glycols can also be used, although their use is limited due to the elevated nitrogen concentrations associated with urea and the increase in biochemical oxygen demand that results from glycol use. A variety of Source Cause State DOT Controllable Traction Deicing Application The application of sodium chloride or other chloride salts to reduce skid hazards results in the runoff of applied salts from road surfaces, parking lots, and sidewalks. Partially. Application rates, timing, and compound type are adjustable. However, public safety must always be a priority, and applications on private property and local roads are not controllable by the state DOT. Atmospheric Deposition In coastal areas, saltwater spray can contribute to atmospheric deposition. Volcanic emissions, rainfall, fossil fuel consumption, and wind suspension can also influence elevated chloride levels. No. Saltwater spray is the most significant source and is natural and uncontrollable. Runoff from Stockpiles Organizations in charge of highway maintenance must stockpile salts and other chemicals for traction control. Runoff from these stockpiles contributes to chloride loads if not properly managed. Yes. Stockpiles can be covered, and runoff from stockpiles can be detained and managed on site. Runoff from Adjacent Land Fertilizers, animal waste, dust-control chemicals, and groundwater that is used for irrigation can all contribute to elevated chloride concentrations. No. Topography and local ordinances can play a role in controllability. Table 36. Controllability of primary sources of chloride in the highway environment.

Compliance Strategy Method Components Applicability Critical Considerations Critical Constraints Traction Control Plan Source control Reduce salt application rate, method, or locations of salt application; use of alternative materials; educational programs for operators Cold weather climate in which road salting has been identified as a contributor to chloride loading Identify methodology and consequences of implementing change to traction chemical application. • Public safety • Institutional coordination • Equipment availability Alternative Paving Materials Source control Construction of alternative road surfaces or roadway heating mechanisms Cold weather climates with access to sufficient power or natural sources of heat; key areas, such as bridges, corners, or locations near affected waterways Identify key locations and economic feasibility. • Maintenance • Coordination of construction • Cost Evaporation Ponds Separation, evapotranspiration Retention basin Low runoff volumes Identify available space. • Space • Maintenance • Cost • Accessibility Detention Ponds Flow attenuation, evapotranspiration Detention ponds, bioretention basins Large peak flows, appropriate dilution factor in receiving water Identify available space. • Space • Dilution ratio in receiving water • Availability of salt-tolerant species • Cost • Maintenance • Accessibility Table 37. Chloride compliance strategies.

Compliance Strategies Approach 69 agricultural by-products—such as those from beet juice, molasses, and milk processing—have also been investigated for use in deicing applications in recent decades (Fay and Shi 2012). Field tests conducted on some of these by-products have shown promise in anti-icing applications, with the Michigan Department of Transportation reducing rock salt use in the test area by 28 percent in one season and 38 percent in another season (Kahl 2002). Structural Best Management Practices Applicable Treatment Processes: Evaporation, attenuation. The cost-effective options to remove chloride from water are limited. Most BMPs for chloride involve retention or capture of chloride, rather than actual removal. One effective way to remove chloride ions from water is to precipitate them out of solution by re-forming salts through evaporation. Runoff could be diverted into evaporation ponds, where it would be stored until the summer months when it is warm enough for the water to evaporate (Golub et al. 2008). This option is only viable for areas with low runoff volumes, and it would require that dried salts are removed after evaporation. Retention ponds could also be used in meeting chloride TMDLs by capturing peak flows and slowly releasing them over time to reduce the peak chloride loads to receiving waters. When retention is selected as a chloride-control strategy, a thorough evaluation of potential ground- water contamination should be performed (Clark and Pitt 2007). However, these by-products have also caused increased BOD. Therefore, the state DOT should consider the trade-offs from substituting one POC for another. Bioretention filters are not likely to remove chloride ions, as both soil and chloride ions are negatively charged. Although bioretention systems may delay the release of chloride ions, this retardation is only temporary, and the retained chloride ions are subsequently released (Denich et al. 2013). Table 37 is a summary of the chloride compliance strategies and the factors that should be considered during the evaluation.