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136 CHAPTER 4 SUMMARY OF IDENTIFIED RESEARCH GAPS AND NEEDS The survey of state departments of transportation (DOTs) final presentation of itemized research needs statements shown water quality practitioners and the review of available research in Table 4-1. and ongoing studies revealed several potential research gaps The individual research categories have been ranked and with regard to highway runoff water quality management and sorted (on a scale from 1 to 5) according to DOT research pref- receiving waters impacts. Research categories were identi- erences, results from the literature review, and opinions of pro- fied within the five main topic categories: Brief Review of fessional investigators. The itemized research needs state- Major Recent Syntheses of Highway Runoff/Urban Storm- ments beneath each individual research category have been water Quality Research, Evaluation of Stormwater Control organized, in some cases according to the logical progression Facilities and Programs, Watershed-Based Approaches, High- of research activities and in other cases according to the per- way Runoff Characterization and Assessment, and Receiving ceived priority of the research team. Based on the top-ranking Waters Impact Assessment. Many of these research categories research topic areas, 14 research project statements--including span two or more of the main topic categories, so they were necessary tasks, timeline, and approximate budget--have been combined for a total of 33 individual research categories in the prepared and included in this report's Summary section.

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137 TABLE 4-1 Ranked and sorted listing of identified gaps and needs in highway runoff water quality research Ranking Itemized Research Needs Based on Research DOT Literature Team's Ranking Review Ranking NCHRP Panel Recommended Research Needs n/a Evaluation of the impacts and implication of TMDLs on DOTs BMP Maintenance and Longevity Development of contract administration of BMP requirements and contractual methods to improve BMP implementation Compilation of BMP maintenance and lifetime effectiveness information Cost-benefit analysis of BMP maintenance practices Guidance for estimating life-cycle costs of BMPs that account for maintenance required for continually functioning and efficient BMPs Development of nationally applicable BMP operations and maintenance guidance (maintenance frequencies, logistics and personnel requirements, estimates based on 5 5 5 influent characteristics and site conditions) Development of methods for increasing longevity and minimizing maintenance requirements of infiltration BMPs Evaluation of sediment toxicity as a function of maintenance frequency Evaluation of issues and methods of disposing or reusing BMP maintenance-generated wastes Evaluation of designs and maintenance of BMPs to reduce conflicts with endangered and threatened species Information Sharing and Technology Exchange Systems Compilation of major syntheses of stormwater runoff research and guidance into a master bibliographic database Development of a stormwater runoff and BMP performance and design database specific to highways 4 5 5 Development of an information sharing system for highway runoff research documents and monitoring data Identification and guidance of practical and accepted monitoring methods for highway runoff Watershed Planning Development and evaluation of techniques to integrate transportation-related runoff analysis into overall watershed management Development of standard methods, models, and data for establishing critical needs within a watershed to prioritize areas for retrofit and BMP implementation Development of geomorphologic models for estimating watershed development impacts on receiving streams Quantification and development, or both, of indices and indicators of the contribution 4 5 4 of state highway infrastructure relative to total impervious surface area in a watershed Evaluation of the ability of watershed or regionally based enhancements of wet weather storage capacity to improve baseline (high and low flow) hydrology and ecological productivity downstream Characterization on a watershed basis and the availability and prioritization of sites for constructed wetlands and wet ponds Demonstration of the costs and benefits of alternative/offsite/watershed-based stormwater mitigation Economic Analysis and Assessment of BMPs Guidance on quantifying BMP lifecycle costs and benefits associated with receiving waters protection Evaluation of potential reductions in costs of stormwater treatment through alternative siting within the watershed Evaluation of the BMP benefits and constraints in highly urbanized corridors 5 4 5 Cost comparisons of BMP treatment trains, distributed BMPs, and regional BMP systems Development of BMP cost estimation tools that account for land value, site constraints, construction, operations, and maintenance, as well as receiving waters protection, aesthetics, and infrastructure savings on conventional drainage structures Cost estimates for nonstructural BMPs General BMP Evaluation and Selection Development of standard performance measures for BMP efficiency 4 4 4 Development of an expert system for BMP selection and design Assessment of and design guidance for ultra-urban BMPs (continued on next page)

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138 TABLE 4-1 (Continued) Ranking Itemized Research Needs Based on Research DOT Literature Team's Ranking Review Ranking Low Impact Development (LID)/Distributed BMPs Development of LID design strategies, performance standards, and specifications Documentation of LID's applicability , efficacy, and long-term economic sustainability for transportation systems 4 4 4 Evaluation of the type of hydrologic losses that can be achieved under various climatic, soil, slope, and vegetation conditions LID modeling and design guidance for accurately sizing end-of-pipe control systems Development of methods and technologies to promote the reuse of stormwater Design Variables Affecting BMP Performance Evaluation of design variables that are related to biochemical and geochemical treatment mechanisms 3 5 4 Conduct of pilot-scale experiments that evaluate the relation of various design variables on BMP performance BMP Modeling Evaluation of modeling approaches and guidance on model selection and application Pilot experiments to collect data needed for parameter estimation and model calibration Development of unit treatment models that incorporate sorption, biodegradation and uptake, photolysis, and volatilization 3 5 4 Development of models for simulation of BMP treatment trains Development of BMP treatment models that account for treatment efficiency losses over time Development or evaluation of models that can be used for modeling pollution plumes in BMPs Hydraulic Assessment of BMPs Evaluation of the characteristics and effects of short-circuiting, bypass, and overflow Evaluation of the nature of correlation between hydraulic residence time and performance 3 4 4 Development of methods or models for estimating the true hydraulic residence in stormwater ponds Development of methods to optimize detention basin design to maximize treatment Methods to Improve Pollutant Removal in Existing Stormwater Systems Cost­benefit analysis of alternative flood control retrofits with consideration of overall feasibility and potential impacts to flood control Risk assessment of alternative, less conservative flood control methods through the use of continuous runoff simulation modeling Development of detailed design guidance for flood control retrofits Evaluation of the effectiveness of BMP retrofits Development of recommendations for soil amendments for use in BMPs to passively improve performance 3 4 4 Development of methods for improving and maintaining hydraulic conductivity of infiltration-based stormwater control facilities Evaluation of the effectiveness of combination of sedimentation, filtration, and chemical addition for stormwater BMP construction projects Evaluation of the potential impacts of coagulants to receiving waters Detailed guidance for areas that require coagulant use to meet water quality objectives Development of new technologies and improvements on existing designs to increase the removal of high-priority pollutants Sedimentation and Turbidity Impacts Development of new exposure metrics that account for sublethal effects (as opposed to direct mortality) Examination of the effects of frequent short-term pulses of suspended sediment Need for additional research on correlations between particle size, shape, and composition of sediments to fish sensitivity Evaluation of the relationships between seasonal timing and effect of sediment load Evaluation of the applicability of the knowledge of fish survival responses to turbid 3 4 4 flows to the development of mixing zones, work windows, treatment systems, and buffers that will allow fish to perform their necessary life functions during project construction and operation Identification of practical means of controlling turbidity Development of hydromodification measures (estimated downstream hydrological changes) and then measures for assessing potential downstream channel and bank instability.

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139 TABLE 4-1 (Continued) Ranking Based on Research Itemized Research Needs DOT Literature Team's Ranking Review Ranking Erosion and Sediment Control Evaluation of the effectiveness of erosion controls at removing fine particulates Evaluation of the effectiveness of using polyacrylamides or other flocculants in conjunction with other sedimentation and erosion control practices Development of techniques to increase germination, soil coverage, and survival rates of native vegetation Evaluation and comparison of the different types of vegetation for riprap planting Research on the necessary "top elevation" for conventional riprap as a function of velocity, turbulence, and flow duration Comparison of terraced versus sloping riprap in terms of hydraulic performance and planted vegetation success Evaluation of alternative bank stabilization techniques that have a lesser effect on riparian and aquatic habitat than riprap Detailed inspection of riprap where vegetation is now growing or has grown, to better 4 3 3 understand its impacts on bank stability Guidance for seed mixes and effective establishment and maintenance of erosion control vegetation for short-term first growth and long-term establishment Evaluation of potential water quality impacts of soil stabilizers used in erosion control Development of standard, approved postconstruction erosion control inspection and enforcement programs Evaluation of slope and soil conditions necessary for vegetation establishment Evaluation of new and innovative erosion control technologies Evaluation of erosion control methods for arid regions Evaluation of the performance of nonvegetative permanent soil stabilizers for reducing erosion and potential water quality impacts Development and evaluation of temporary nonvegetative soil stabilization techniques General Constituent Characterization of Highway Runoff Characterization of chemical constituents not monitored generally, but believed to be present frequently in highway runoff 3 3 3 Evaluation of representative methods for monitoring and analyzing oil and grease and total petroleum hydrocarbons Atmospheric Deposition Studies that directly relate highways and transportation systems to atmospheric deposition Development of methods to evaluate the contribution of atmospheric deposition to 3 3 3 highway runoff pollution Evaluation of the fractions of pollutants contributed by atmospheric deposition for different land uses and classes of contaminants First Flush Characterization Adoption of a standardized method for defining and identifying first flush phenomena Development of a list of highway runoff pollutants that tend to exhibit a first flush Evaluation of toxicity of road surface runoff from different phases of a runoff event 3 3 3 Correlation of toxicity with respect to pollutographs and hydrographs Evaluation of the effects of watershed characteristics on first flush phenomena Evaluation of BMPs designed to capture the first flush Impacts of Highway Construction and Vegetation Maintenance Activities Standardization of suspended-sediment measurement and reporting methods Development of screening methods for assessing the quality of site soils on a grain-size basis as to determine the level of monitoring as well as sediment and erosion controls necessary to prevent impacts to receiving waters Herbicide runoff characterization and toxicity assessments 3 3 3 Guidance on maintenance facility BMP design Development of guidance for fertilizer utilization for seeding and turf establishment near sensitive water bodies (nutrient runoff prevention) Equipment testing methods and performance assessment of mechanical and mechanical/vacuum sweepers Stream Crossings Examination of the water quality effects of maintenance practices through field studies Development of bridge deck runoff quality constituents database Examination of the potential risks associated with hazardous materials spills 3 3 3 Evaluation of how bridge design and average daily traffic affects runoff quality Assessment of potential receiving water temperature changes and mitigation Development and evaluation of BMPs and standards for abating receiving water temperature impacts (continued on next page)

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140 TABLE 4-1 (Continued) Ranking Based on Research Itemized Research Needs DOT Team's Literature Ranking Review Ranking Unit Treatment Processes Characterization and evaluation of the fundamental treatment processes within different BMP types Pilot-scale experiments for the collection of data on unit treatment processes for various BMP types Compilation and assessment of available unit treatment processes data Research to obtain within storm data on BMP effectiveness to assess short-term 2 4 3 pollutant issues and collect unit treatment processes information Evaluation of metals fractionation under anaerobic and anoxic conditions Development of the ability to accurately measure and analyze unit treatment processes Evaluation of BMP design and performance with respect to particle size distribution in stormwater runoff and associated metals Evaluation of the physical, chemical, and biological treatment processes of BMPs Toxicity and Bioassessment Development of standardized toxicity and bioassessment methods for assessing impacts of highway runoff on receiving water systems Evaluation of the parts of storm events that are most toxic to receiving waters Assessment of BMP performance in terms of toxicity reduction or other biological 2 4 3 impact indicator Guidance on BMP selection based on toxicity Evaluation of chemical, physical, and toxicity impacts to aquatic biota of stormwater discharges Evaluation of viral pathogen indicators and development of treatment options Fate and Transport of Highway Runoff Constituents Identification of sediment sources and evaluation of transport rates and residence time of sediment in highway runoff, treatment facilities, and receiving waters Evaluation of sediment transport mechanics and blockage at inlets, junctions, and transitions in full and partly full conduits Comprehensive studies on the effects of soils, topography, land use, and various storm hydrographs on sediment yield 2 4 3 Evaluation of nutrient leaching and the sorption and desorption processes of roadside soils Development of predictive models that consider runoff/storm relationships, particularly storm scour and redeposition Characterization of the bioavailable fraction of dissolved metals and trace organics in highway runoff Market-Driven Approaches: BMP Asset Management and Pollutant Trading Research into the practicality of pollutant trading as a viable approach to highway runoff management 2 4 3 Enhancement of maintenance management systems to facilitate asset management of BMPs Gross Pollutant Removal/Drain Inlet Studies Evaluation of the effectiveness and limitations of source controls at reducing gross solids in highway runoff (e.g., public education, catch basin cleaning, and street sweeping) Development of a standard method for measuring and reporting gross solids and its components 2 4 3 Development of modeling and estimation techniques for gross solids Evaluation of the impacts of gross solids in highway runoff Evaluation of leaching or sorption, or both, capacity of pollutants captured in catch basins Guidance on gross solid removal device design and performance Pollutant Retention in BMPs Investigation of the potential for leaching or resuspension of previously captured pollutants Investigation of how changes in pH, oxidation-reduction potential, hardness, and 2 3 3 organic content may affect desorption or dissolution, or both, of captured pollutants Assessment of the long-term ability of BMPs to keep pollutants sequestered Bioavailability of pollutants in the sediments of wet ponds and wetlands used for highway stormwater treatment

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141 TABLE 4-1 (Continued) Ranking Based on Research Itemized Research Needs DOT Literature Team's Ranking Review Ranking Water Quality Runoff Modeling Forward-looking data collection efforts that focus more on new parameters that may be required by models of the future Development of hybrid models that take advantage of both stochastic and deterministic methods in order to produce models that have the benefits of both statistical and simulation-based models 2 3 3 Adaptation of agricultural models for herbicide and pesticide modeling Extension and enhancement of existing models to simulate a wider range of contaminants Evaluation of the validity of build-up and washoff as a method of estimating pollutant loads Cold-Weather Studies Guidance on monitoring roadside snow as well as snowmelt runoff Development of modeling methods for estimating snowmelt runoff events Evaluation of the performance and feasibility as well as maintenance issues of stormwater BMPs during cold weather Assessment of deicing agent and traction sand impacts on receiving water bodies 2 3 3 Guidance on the management and storage of snow removed from urban highways to minimize impacts of snow storage area runoff Development of deicing agent selection criteria based on cost, effectiveness, and potential environmental impact Guidance and methods for applying the minimum amount of deicing chemicals and traction sand necessary to maintain safe road conditions Modeling of Water Quality Impacts to Receiving Waters Need for research and data to support model parameter estimation Guidance on water quality model selection 2 3 3 Development of stochastic water quality models Development of models that predict pollutant bioavailability and toxicity BMPs Vector Control Evaluation of public health impacts of various stormwater management alternatives 2 3 3 Evaluation of maintenance and design methods for controlling mosquitoes and other vectors in highway BMPs Runoff Characterization with Independent Variable Correlation Better characterization of constituents associated with different-sized particles in highway runoff, particularly heavy metals, nutrients, and hydrocarbons Evaluation of statistically valid traffic volume-related studies Development of correlations between storm event intensity and duration with constituent levels 3 2 3 Identification of statistically significant differences in concentrations in relation land use type alone Runoff quality characterization according to the various highway classifications (e.g., urban, rural, on-ramps, off-ramps, and total impervious area) Establishment of traffic thresholds beneath which certain pollutants in highway runoff can be considered negligible or irreducible Wetlands Impacts Compilation and analysis of available water quality, sediment quality, and bioassessment data for wetlands receiving runoff from highway facilities 3 2 3 Development of indicators for assessing impacts to wetlands from highway runoff by conducting a detailed analysis of currently available data on wetlands receiving runoff from highway facilities Public Perception/Aesthetics of BMPs Conduct of public opinion surveys to assess the public's perception of stormwater management, in general, and BMPs, in particular 1 3 2 Guidance on how to improve public perception of various types of BMPs Quantification of BMP impacts to property values and evaluation of methods to improve aesthetics and multiuse functionality Impacts of Highway Construction and Repair Materials Compilation of properties data for highway construction and repairs materials Evaluation of the speciation, bioavailability, and toxicity of metals in highway construction material leachate 1 3 2 Evaluation of the effects and influence of temperature on the leachings of pollutants from construction materials Evaluation of the capabilities of existing BMPs to mitigate impacts from highway construction material contamination (continued on next page)

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142 TABLE 4-1 (Continued) Ranking Itemized Research Needs Based on Research DOT Literature Team's Ranking Review Ranking Groundwater Quality Analysis and Impacts Development of a standardized procedure for monitoring and assessing soil and groundwater impacts caused by infiltration facilities Evaluation of the pollutant retention capacities of different soil types and geological conditions Evaluation of the potential groundwater impacts of soluble highway runoff pollutants such as herbicides, nutrients, deicing agents, petroleum hydrocarbons (e.g., BTEX), and 2 2 2 gasoline oxygenates Determination of the sources of MTBE in groundwater Development of approaches to addressing groundwater contaminants introduced to surface waters from dewatering operations Development of infiltration guidance to prevent groundwater contamination Water Quality Impacts of Combined Sewer Overflows (CSOs) Hydraulic assessment of highway runoff contributions to CSOs impacts to receiving waters. Better monitoring of CSOs effluent quality in relation to meteorological factors 1 1 1 Evaluation of the prevailing conditions or factors that increase or decrease CSOs impacts Development and evaluation of practices (structural and nonstructural) to mitigate CSOs impacts