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IDENTIFICATION OF RESEARCH NEEDS RELATED
TO HIGHWAY RUNOFF MANAGEMENT
SUMMARY The purpose of research project NCHRP 25-20(02) is to identify and describe
research projects that address priority needs in the area of highway runoff management
and control. This project was designed to conduct a broader search of the available data
and studies than was accomplished by NCHRP Project 25-20 and to identify state
departments' of transportation (DOTs) research activities and priority research areas
for improving the quality of stormwater runoff. This report provides an updated and
thorough list of research needs that can be used in the decision-making and prioritiza-
tion processes regarding funding of future research.
State DOT research directors and water quality professionals were contacted to
locate existing research and research-in-progress and to list what they believed were
the most important remaining needs related to research on water quality control and
stormwater impacts on receiving waters. DOT water quality professionals--includ-
ing engineers, National Pollutant Discharge Elimination System (NPDES) special-
ists, and other program managers--from all 50 states participated. The DOTs
expressed the strongest needs and interests in the area of cost and performance of
stormwater control facilities or best management practices (BMPs). The DOTs' top
interests paralleled gaps in the literature in most cases; where such gaps were not
identified in the literature but where DOT interest was high, mechanisms for infor-
mation sharing are needed. A combined literature review, DOT preferences, and
research team recommendations are itemized in Table 4-1 of this report. The research
needs identified through the DOT survey, literature review findings, and the opinions
of the stormwater experts involved in this investigation were prioritized by rank on
a scale from 1 to 5.
RESEARCH GAPS AND NEEDS
The following paragraphs summarize the conclusions of the investigation. A brief
discussion of the research gaps and needs identified in the literature is presented, fol-
lowed by the literature review and itemized research statements identified by DOTs as
research needs. Some research statements span multiple research categories and likely
would be combined into single projects.
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BMP Maintenance and Longevity
A compilation of the results of current studies on BMP operations and maintenance
is needed, potentially in the form of a nationally applicable manual on BMP operations
and maintenance, with guidance on estimating maintenance frequencies based on influ-
ent characteristics and site conditions. The costs of BMP maintenance are not factored
in during the initial planning and BMP selection phases of construction projects. Agen-
cies often lack the tools to make good estimates of the staff-hours needed to adequately
maintain BMPs. Guidance on estimating life-cycle costs of BMPs appears to be needed.
Finally, there is a need for further development of methods to increase the longevity
and minimize maintenance requirements of infiltration BMPs, such as the use of pre-
settling basins or polyacrylamides to maintain infiltration rates.
With regard to sedimentation, research is needed to evaluate sediment toxicity as
a function of maintenance frequency and methods for disposing or reusing BMP
maintenance-generated wastes. See section 3.2.11 for a discussion on BMP maintenance
and longevity.
Itemized Research Needs
1. Development of contract administration of BMP requirements and contractual
methods to improve BMP implementation,
2. Compilation of BMP maintenance and lifetime effectiveness information,
3. Costbenefit analysis of BMP maintenance practices,
4. Guidance for estimating life-cycle costs of BMPs that account for maintenance
required for continually functioning and efficient BMPs,
5. Development of nationally applicable BMP operations and maintenance guidance
(maintenance frequencies, logistics and personnel requirements, estimates based
on influent characteristics and site conditions),
6. Development of methods for increasing longevity and minimizing maintenance
requirements of infiltration BMPs,
7. Evaluation of sediment toxicity as a function of maintenance frequency,
8. Evaluation of issues and methods of disposing or reusing BMP maintenance-
generated wastes, and
9. Evaluation of designs and maintenance of BMPs to reduce conflicts with endan-
gered and threatened species.
Information Sharing and Technology Exchange
A compilation of major syntheses extracted from stormwater runoff research is needed
to support, encourage, and facilitate a more efficient and comprehensive exchange of
information among stormwater professionals. This report, and that of the National
Highway Runoff Data and Methodology Synthesis (NDAMS), presents a good start-
ing point for such a compilation. The International Stormwater BMP Database pri-
marily contains BMP design and monitoring data but makes no direct links to published
literature. A research project linking an extensive bibliographic database, such as a
refined and value-added NDAMS database, to a water quality and BMP performance
database, such as the International Stormwater BMP Database, would create a useful
tool for stormwater practitioners. See section 3.1.1 in this report for a synthesis of
recent major highway runoff research.
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Itemized Research Needs
1. Compilation of major syntheses extracted from stormwater runoff research and
linkage into a master bibliographic database;
2. Development of a stormwater runoff research database and a BMP performance
and design database specific to highways using the International Stormwater
BMP Database as a model;
3. Development of an information-sharing system that links the two databases listed
in item 2 into an online, user-friendly database for data entry and retrieval; and
4. Identification of and guidance on practical and accepted monitoring methods for
highway runoff.
Watershed Planning
Although much literature supporting watershed management exists, there is still a need
for the development and evaluation of techniques to integrate transportation-related
runoff analysis with overall watershed management. Stream channels respond to changes
in flow volume and sediment loading, which subsequently produce recognizable patterns
and forms. Watershed change is known to have a corresponding effect on channels lead-
ing to bank erosion and head cutting. Although these processes are well understood and
descriptions of channel morphology are well developed, effective predictive models of
channel geomorphic response are lacking. Correspondingly, research to support devel-
opment of regulatory structure more appropriate to the episodic nature of runoff also is
needed, along with identification of indices and indicators specific to transportation-
related runoff. See section 3.3.1 for a discussion on watershed planning.
Itemized Research Needs
1. Development and evaluation of techniques to integrate transportation-related
runoff analysis into overall watershed management;
2. Development of standard methods, models, and data for establishing critical
needs within a watershed to prioritize areas for retrofit and BMP implementation;
3. Development of geomorphologic models for estimating watershed development
impacts on receiving streams;
4. Quantification or development, or both, of indices and indicators of the contribu-
tion of state highway infrastructure relative to total impervious surface area in a
watershed;
5. 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;
6. Characterization of the availability and prioritization of sites on a watershed basis
for constructed wetlands and wet ponds; and
7. Demonstration of the costs and benefits of alternative, off-site, and watershed-
based stormwater mitigation.
Economic Analysis and Assessment
The review of literature pertinent to the economic analyses and assessment of BMPs
revealed cost estimation information for nearly all proprietary BMPs and most of the
common nonproprietary structural BMPs. For a number of BMP types, cost regression
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equations have been developed that are primarily based on imperviousness, land use,
and flow rates and volumes; however, life-cycle costs, opportunity costs, and external-
ities often are neglected in cost estimation. There is a need to develop BMP cost esti-
mation tools that account for land value, site constraints, construction, operations, and
maintenance, as well as receiving waters protection, aesthetics, and infrastructure sav-
ings on conventional drainage structures. Quantification of benefits from receiving
waters protection requires the use of existing water quality, habitat, and bioassessment
monitoring data for both the runoff and receiving waters.
Costs associated with public education, catch basin maintenance, and roadside veg-
etation control activities would aid in the optimization and adequate allocation of
stormwater management funds. Cost evaluations and comparisons of BMP treatment
trains, distributed BMPs, and large centralized regional BMP systems also are needed.
See section 3.2.14 for a discussion on economic analysis and assessment of BMPs.
Itemized Research Needs
1. Guidance on quantifying BMP life-cycle costs and benefits associated with
receiving waters protection;
2. Evaluation of potential cost reductions of stormwater treatment through alterna-
tive siting within the watershed;
3. Evaluation of the BMP benefits and constraints in highly urbanized corridors;
4. Cost comparisons of BMP treatment trains, distributed BMPs, and regional BMP
systems;
5. Development of BMP cost-estimation tools that account for land value, site con-
straints, construction, operations, and maintenance, as well as receiving waters
protection, aesthetics, and infrastructure savings on conventional drainage struc-
tures; and
6. Cost estimates for nonstructural BMPs.
General BMP Evaluation and Selection
There are many different ways to evaluate BMPs. The most common methods mon-
itor the effluent and influent water quality with the primary goal of estimating BMP
efficiency. Several methods exist for monitoring, analyzing, and reporting BMP effi-
ciency. The most common methods include the efficiency ratio, summation of loads,
regression of loads, mean concentration, efficiency of individual storm loads, reference
watersheds, and before-and-after studies. More recent methods include effluent prob-
ability, flow-dependent removal efficiency, minimum influent concentration, and the
pollutant flux ratio. Of all these methods, the most promising for the consideration of
standard BMP efficiency are the effluent probability method, which is recommended
in Urban Stormwater BMP Performance Monitoring: A Guidance Manual for Meet-
ing the National Stormwater BMP Database Requirements (GeoSyntec Consultants,
2002), and the minimum influent concentration removal efficiency methods, referred
to in the Stormwater Best Management Practice Demonstration Tier II Protocol for
Interstate Reciprocity (2001). The former provides greater detail on the actual perfor-
mance of a BMP; the latter provides an easier way to understand the transferable
measure of BMP efficiency. However, neither method can be used to estimate
adequately the efficiency of BMPs without well-defined inlets and outlets, such as
infiltration-type facilities or source controls. Reference watersheds and before-and-
after studies are used often in these situations.
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Because there are so many methods available for evaluating and reporting the effi-
ciency of BMPs, consensus and guidance clearly are needed. Selection of BMPs often
is based on performance claims and reported efficiencies in relation to water quality
goals, but many other factors are involved, including budgetary and site constraints,
which include available land, climate, soil and vegetation conditions, topography, sur-
rounding land use, and local regulatory issues. All of these factors make it difficult to
select and design BMPs. As stated in the GKY Synthesis and Research Plan, "[p]rac-
titioners need quick and ready access to BMP information and a means of quickly
applying applicable portions of it to site-specific situations--an expert system." This
current effort agrees that such an "expert system" is needed to aid in the selection and
design of highway stormwater BMPs. See section 3.2.1 for a discussion on general
BMP evaluation.
Itemized Research Needs
1. Development of standard performance measure(s) for BMP efficiency,
2. Development of an expert system for BMP selection and design, and
3. Assessment of and design guidance for ultra-urban BMPs.
Low-Impact Development and Distributed BMPs
Pilot projects conducted by several researchers have demonstrated the potential of
low-impact development (LID) to meet regulatory requirements, but substantial work
needs to be conducted on developing LID design strategies, performance standards, and
specifications. LID's decentralized approach to stormwater management technology
has tremendous potential to supplement, or in some situations completely replace, con-
ventional centralized stormwater BMP approaches. However, LID's applicability, effi-
cacy, and long-term economic sustainability for transportation systems have yet to be
determined or documented. A long-term research need is to document the type of
hydrologic losses that via LID can be achieved regionally and under various climatic,
soil, slope, and vegetation conditions. See section 3.2.9 for a discussion on LID.
Itemized Research Needs
1. Development of LID design strategies, performance standards, and specifications;
2. Documentation of LID's applicability, efficacy, and long-term economic sus-
tainability for transportation systems;
3. Evaluation of the type of hydrologic losses that can be achieved under various cli-
matic, soil, slope, and vegetation conditions;
4. LID modeling and design guidance for accurately sizing end-of-pipe control sys-
tems; and
5. Development of methods and technologies to promote the reuse of stormwater.
Design Variables Affecting BMP Performance
Primary design variables affecting BMP performance are those that control flow.
These include outlet structures, baffles, berms, and vegetation density, in addition to
the total volume a system is able to capture. Design features specific to individual types
of BMPs, such as specific surface area for detention facilities and flow length for swales,
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also are significant factors to consider when evaluating and comparing BMP perfor-
mance. These design variables are related directly to physical treatment mechanisms of
sedimentation and filtration. Variables related to the biochemical and geochemical treat-
ment mechanisms, such as vegetation and soil type, also may be important design fac-
tors; however, no studies were found that compared BMP performance according to these
variables, indicating a potential research gap. Before sufficient field data are available to
make assessments of design variables that influence treatment, pilot-scale experiments
can be conducted to ascertain some of the needed design and performance information.
See section 3.2.7 for a discussion of design variables affecting BMP performance.
Itemized Research Needs
1. Evaluation of design variables that are related to biochemical and geochemical
treatment mechanisms, and
2. Execution of pilot-scale experiments that evaluate the relation of various design
variables on BMP performance.
BMP Modeling
With regard to BMP modeling, the unit processes of sedimentation and infiltration
appear to be well covered in the literature. However, other BMP water quality treat-
ment unit processes such as sorption processes (absorption and adsorption), biodegra-
dation and uptake, photolysis, and volatilization still need further study before reli-
able BMP performance models can be developed. Information on the modeling of
BMP treatment trains appears to be lacking as well. A better understanding of BMP
longevity and the decrease in the treatment efficiency as a function of time are
required so that the optimization models that are used to select cost-effective BMP
systems can provide better estimates of the lifetime costs and benefits of BMPs. How
sources of pollutants are represented in models also merits further exploration. Many
models still use a "build-upwash-off" approach as the only way the pollutants get
into stormwater, which can lead to faulty results if the BMP acts directly on that func-
tion. The development of a review of modeling approaches and guidance on their
selection and application would be a useful resource for stormwater practitioners. See
section 3.2.10 for a discussion of BMP modeling.
Itemized Research Needs
1. Evaluation of modeling approaches and guidance on model selection and
application;
2. Use of pilot experiments to collect data needed for parameter estimation and
model calibration;
3. Development of unit treatment models that incorporate sorption, biodegradation
and uptake, photolysis, and volatilization;
4. Development of models for simulation of BMP treatment trains;
5. Development of BMP treatment models that account for treatment efficiency
losses over time; and
6. Development or evaluation of models that can be used for modeling pollution
plumes in BMPs.
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Hydraulic Assessment
Based on the review of literature with regard to the hydraulic assessment of storm-
water control facilities in relation to BMP performance, the most pressing gaps
appear in the evaluation of the characteristics and effects of short-circuiting and
bypass or overflow (e.g., ponds or wetlands discharging over the low-flow outlet or
bioswales when depths and velocities for good treatment are exceeded). The influ-
ence of hydraulic residence time on BMP performance has been well studied, and it
has been confirmed that detention time correlates positively with pollutant removal
(at least for particulate-bound pollutants). However, no studies were found that inves-
tigated the nature of the correlation (linearly, asymptotically, etc.). Also, hydraulic
residence is calculated usually by dividing the permanent pool volume by the average
outflow discharge rate of a BMP. The true hydraulic residence time depends on the
flow path through the system, which requires some means of estimating the velocity
field of the system such as the use of tracers, ultra-sensitive velocity meters, or two-
and three-dimensional hydrodynamic models. See section 3.2.3 for a discussion on
hydraulic assessment.
Itemized Research Needs
1. Evaluation of the characteristics and effects of short-circuiting, bypass, and
overflow;
2. Investigation of the nature of the correlation between detention time and pollu-
tant removal;
3. Development of methods or models for estimating the true hydraulic residence
in stormwater ponds; and
4. Development of methods to optimize detention basin design to maximize
treatment.
Methods to Improve Pollutant Removal in Existing Stormwater Systems
One promising method to improve pollutant removal in existing stormwater systems
is detailed design guidance that includes overall feasibility costbenefit comparisons
between retrofit alternatives and potential impacts to flood protection. Another need is
to sponsor research to evaluate if other less-conservative flood control methods--such
as the use of more-refined continuous simulation approaches to assess flood detention
needs--could be employed safely.
With regard to coagulants, the reviewed literature (as well as the plethora of litera-
ture available in the area of wastewater management) suggests that further research in
this area is unlikely to be a high priority. However, in selected locations, coagulant use
may be necessary to achieve water quality goals, thus more detailed guidance on design
for highway situations may be valuable. Potential impacts to receiving waters from
coagulant use may warrant further research, particularly for stormwater treatment prod-
ucts (either new products or ones not used widely--such as chitosan). Recommenda-
tions for soil amendments to use in BMPs to more passively improve performance also
are areas for potential research. See section 3.2.5 for a discussion on methods to
improve pollutant removal in existing stormwater systems.
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Itemized Research Needs
1. Costbenefit analysis of alternative flood control retrofits with consideration of
overall feasibility and potential impacts to flood control;
2. Risk assessment of alternative, less-conservative flood control methods through
the use of continuous runoff simulation modeling;
3. Development of detailed design guidance for flood control retrofits;
4. Evaluation of the effectiveness of BMP retrofits;
5. Development of recommendations for soil amendments for use in BMPs to pas-
sively improve performance;
6. Development of methods for improving or maintaining hydraulic conductivity
of infiltration-based stormwater control facilities;
7. Evaluation of the effectiveness of combining sedimentation, filtration, and chem-
ical addition for stormwater BMP construction projects;
8. Evaluation of the potential impacts of coagulants to receiving waters;
9. Detailed guidance for areas that require coagulant use to meet water quality
objectives; and
10. Development of new technologies or improvements on existing designs to
increase the removal of high-priority pollutants.
Sedimentation and Turbidity Impacts
With regard to sedimentation and turbidity impacts to fish in general and salmonids
in particular, some of the significant research needs identified by Bash et al. (2001)
include (1) developing new exposure metrics that account for sublethal effects (as
opposed to direct mortality); (2) examining the effect of frequent short-term pulses of
suspended sediment; (3) conducting additional research on correlations between parti-
cle size, shape, and composition of sediments to fish sensitivity; (4) studying relation-
ships between seasonal timing and effect of sediment load; and (5) determining whether
knowledge of survival responses to turbid flows can be used to develop mixing zones,
work windows, treatment systems, and buffers that will allow fish to perform their nec-
essary life functions during project construction and operation. See section 3.5.3 for a
discussion of sedimentation and turbidity impacts.
Itemized Research Needs
1. Development of new exposure metrics that account for sublethal effects (as
opposed to direct mortality);
2. Examination of the effects of frequent short-term pulses of suspended sediment;
3. Additional research on correlations between particle size, shape, and composi-
tion of sediments to fish sensitivity;
4. Evaluation of the relationships between seasonal timing and the effect of sedi-
ment load;
5. Evaluation of the applicability of the knowledge of fish survival responses to
turbid flows to the development of mixing zones, work windows, treatment sys-
tems, and buffers that will allow fish to perform their necessary life functions
during project construction and operation;
6. Identification of practical means of controlling turbidity; and
7. Development of hydromodification measures (estimated downstream hydrolog-
ical changes) and measures for assessing potential downstream channel and
bank instability.
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Erosion and Sediment Control
With regard to temporary vegetation controls, sufficient research appears to be avail-
able on the erosion control effectiveness of compost and mulch, erosion control mats
and blankets, and cellular confinement technologies. Adequate guidance exists as well
(see Appendix B for a list of selected guidance manuals). Erosion control effectiveness
for removing fine particulates does not seem to be covered adequately in the literature.
However, the use of polyacrylamides or other flocculants in conjunction with tempo-
rary vegetation controls holds promise for controlling erosion of fine particulates.
More research may be needed on ways to increase germination and survival rates of
native vegetation. With regard to bank protection, research is needed to investigate the
feasibility and performance of vegetated riprap and alternative bank stabilization designs
that minimize impacts to riparian habitat. NCHRP 24-19, expected in 2004, will help to
fill this gap. See section 3.2.6 for a discussion of erosion and sediment control.
Itemized Research Needs
1. Evaluation of the effectiveness of erosion controls at removing fine particulates;
2. Evaluation of the effectiveness of using polyacrylamides or other flocculants in
conjunction with other sedimentation and erosion control practices;
3. Development of techniques to increase germination, soil coverage, and survival
rates of native vegetation;
4. Evaluation and comparison of the different types of vegetation for riprap planting;
5. Research on the necessary top elevation for conventional riprap as a function of
velocity, turbulence, and flow duration;
6. Comparison of terraced versus sloping riprap in terms of hydraulic performance
and planted vegetation success;
7. Evaluation of alternative bank stabilization techniques that have a lesser effect
on riparian and aquatic habitat than riprap;
8. More detailed inspection of riprap where vegetation is growing now or has
grown previously to better understand its impacts on bank stability;
9. Guidance for seed mixes and effective establishment and maintenance of ero-
sion control vegetation for short-term first growth and long-term establishment;
10. Evaluation of potential water quality impacts of soil stabilizers used in erosion
control;
11. Development of standard, approved postconstruction erosion control inspection
and enforcement programs;
12. Evaluation of slope and soil conditions necessary for vegetation establishment;
13. Evaluation of new and innovative erosion control technologies;
14. Evaluation of erosion control methods for arid regions;
15. Evaluation of the performance of nonvegetative permanent soil stabilizers for
reducing erosion and potential water quality impacts; and
16 Development and evaluation of temporary nonvegetative soil stabilization
techniques.
General Constituent Characterization
Many state DOTs have studied highway runoff, so there are several studies available
that generally characterize highway runoff quality. The constituents sampled and the con-
centrations detected do not appear to vary significantly among the studies; therefore, in
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general, characterization of highway runoff does not represent a primary research need.
However, there are gaps in this research for some chemical constituents, including trace
elements--such as polycyclic aromatic hydrocarbons (PAH); benzene, toluene, ethyl-
benzene, and total xylene (BTEX); methyl tert-butyl ether (MTBE); and platinum group
metals--not normally included in characterization studies. See section 3.4.1 for a dis-
cussion on general constituent characterization.
Itemized Research Needs
1. Characterization of chemical constituents not generally monitored but believed
to be frequently present in highway runoff, and
2. Evaluation of methods for monitoring and analyzing oil and grease and total
petroleum hydrocarbons.
Atmospheric Deposition
Based on the review of literature, more studies that relate transportation systems to
atmospheric deposition of pollutants are needed to quantify the contribution of atmo-
spheric deposition to pollutant concentrations found in highway runoff and to gain a bet-
ter understanding of the pollutant sources. Standard methods for evaluating the contribu-
tion of atmospheric deposition to highway runoff should be developed. The contribution
of organic and inorganic pollutants from atmospheric deposition likely differs between
urban and nonurban areas. See section 3.4.3 for a discussion on atmospheric deposition.
Itemized Research Needs
1. Studies that directly relate highways and transportation systems to atmospheric
deposition,
2. Development of methods to evaluate the contribution of atmospheric deposition
to highway runoff pollution, and
3. Evaluation of the fractions of pollutants contributed by atmospheric deposition
for different land uses and classes of contaminants.
First Flush Characterization
There is seemingly a need for the adoption of a standardized method for defining and
identifying first flush phenomena. Some parameters appear to exhibit a first flush, while
others do not. Therefore, a comprehensive list of highway runoff pollutants that tend
to exhibit a first flush may be useful for evaluating receiving water impacts and the fea-
sibility of treating only the first flush of a storm. The current research effort did not find
any studies that investigated specifically how the first flush effect was related to hydro-
logical and watershed characteristics, indicating a potential research gap with regard to
first flush characterization and assessment. See section 3.4.6 for a discussion on first
flush characterization.
Itemized Research Needs
1. Adoption of a standardized method for defining and identifying first flush
phenomena,
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2. Development of a list of highway runoff pollutants that tend to exhibit a first flush,
3. Evaluation of road surface runoff toxicity from different phases of a runoff event,
4. Correlation of toxicity with respect to pollutographs and hydrographs,
5. Evaluation of the effects of watershed characteristics on first flush phenomena, and
6. Evaluation of BMPs designed to capture the first flush.
Impacts of Highway Construction and Vegetation Maintenance
To evaluate erosion control practices, suspended sediment is the primary (and often
the only) parameter monitored during highway construction runoff characterization
studies. It is unclear in the literature whether total suspended solids (TSS) or
suspended-sediment concentrations are being reported; these two terms often are used
interchangeably but may yield vastly different results. There appears to be a need to
evaluate the differences and consequences of using TSS for sediment load calculations
and a need to make stormwater practitioners aware of this potential issue.
Sediment particle-size distribution is an important parameter that is not monitored
frequently. Particle-size distribution plays an important role in the transport and aquatic
biota impacts of mobilized sediment, metals, nutrients, and trace organics. Since mon-
itoring for particle size and other parameters may increase significantly the costs of a
construction project, it would be beneficial to have an initial screening method for
assessing the quality of site soils on a grain-size basis to determine if sediment and ero-
sion controls are necessary to prevent impacts to receiving waters.
Additional work also may be needed in the area of roadside vegetation management.
The potential for herbicides to migrate from roadsides to receiving waters is strongly
dependent on the type of chemical applied (i.e., depends primarily on solubility and
hydrophobicity). Numerous herbicides--only a small number of which have been stud-
ied for their mobility and potential toxicity to aquatic biota--are in use by DOTs
throughout the country. More herbicide runoff characterization studies during storm
conditions are needed as are toxicity studies of the concentrations found. Also, an
analysis of the adsorption of herbicides to various grain sizes would aid in determining
the potential for migration. When more information is available on the potential impacts
of herbicides, a detailed costbenefit comparison of using herbicides (as opposed to
other vegetation control methods, such as manual clearing), should be considered. See
section 3.4.8 for a discussion on the impacts of highway construction and vegetation
maintenance.
Itemized Research Needs
1. Standardization of suspended-sediment measurement and reporting methods,
2. Development of screening methods for assessing the quality of site soils on a
grain-size basis so as to determine the level of monitoring as well as sediment and
erosion controls necessary to prevent impacts to receiving waters,
3. Characterization of herbicide runoff and assessment of toxicity,
4. Guidance on maintenance facility BMP design,
5. Development of guidance for fertilizer utilization for seeding and turf establish-
ment near sensitive water bodies (nutrient runoff prevention), and
6. Equipment testing methods and performance assessment of mechanical and
mechanical/vacuum sweepers.
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5. Develop an Expert System: Incorporate the guidance document into an expert sys-
tem that can be used to guide post-construction BMP selection and design. The
expert system would be able to be customized by individual agencies.
Estimated Project Budget: $450,000 to $550,000; 30 months to complete.
Low Impact Development/Distributed BMPs
LID/Distributed BMPs are gaining increasing attention in the stormwater manage-
ment field and among selected DOTs; however, their functioning in various geographic
conditions and environments is not well known, particularly as applied to highway
environments. LID design guidance is being prepared under NCHRP 25-26. In the
course of this work, additional research needs regarding LID/Distributed BMPs will be
identified. It is likely that these will include
· Documentation of LID's applicability, efficacy, and long-term economic sustain-
ability for transportation systems;
· Evaluation of the type of hydrologic losses that can be achieved under various cli-
matic, soil, slope, and vegetation conditions; and
· Development of methods and technologies to promote the reuse of stormwater.
This area of research was ranked as a relatively high priority by state DOTs and was
included here for that reason; it should be modified based on the results of the ongoing
25-26 project. See section 3.2.9 for a discussion on LID. The research gaps addressed
under this research statement are listed under the Low Impact Development/Distributed
BMPs section of Table 4-1.
Research Objectives
· Conduct a review of LID/Distributed BMPs that are in the ground and operating.
· Conduct an assessment of the types of hydrological losses that can be achieved
under different scenarios of climates, soils, slopes, and vegetative conditions and
an assessment of how the losses will reduce or eliminate downstream impacts of
increased runoff from highway environments.
· Determine feasibility of and conditions for re-use of captured stormwater.
Tasks
1. Perform a Survey and Review of In-the-Ground Applications of LID/Distributed
BMPs: Critically review constructed LID-type projects to assess potential bene-
fits and costs. Interview state DOTs to ascertain what monitoring (water quantity
and quality, as well as visual, maintenance, and problem) has been completed.
Develop a report of case studies and include recommendations for future designs.
2. Conduct a Hydrological Loss Assessment: Unless Task 1 includes some detailed
hydrological monitoring that can be used to ascertain losses from LID-type BMPs,
base the hydrological assessment primarily on the use of existing continuous
simulation models (such as SWMM) to ascertain on regional and national lev-
els what types of runoff hydrological losses can be achieved and how these
reductions in runoff affect potential downstream channel erosion levels. Include
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in the the assessment an evaluation of the site conditions (such as climatic, soil,
slopes, and downstream water body sensitivity) and LID types and level of imple-
mentation necessary to fully or partially mitigate downstream erosional impacts.
3. Develop Potential Water Re-Use Methods and Technologies: Review potential
highway runoff water re-use applications. Develop potential conceptual water
re-use scenarios and evaluate them for potential costs and benefits. Perform long-
term simulation modeling to ascertain the storage size that may be required; eval-
uate the potential for draining the storage to ascertain the costs and benefits.
Estimated Project Budget: $150,000 to $250,000; 18 months to complete.
BMP Design Variables
The effect of BMP design variables on BMP performance is not well understood.
To date, major efforts such as the National Stormwater BMP Database have been able
to confirm only a few of the major design variables that can be shown statistically to
affect BMP performance. The BMP design guidance developed to date has been based
primarily on "good engineering judgment" and on some limited modeling studies. This
research project would develop an approach for conducting more rigorous evaluation
of BMP design versus performance on one or two selected BMP types and would make
recommendations for future evaluations. Research Project 25-20(01) is developing a
unit processes evaluation of BMP performance that should indicate some of the impor-
tant design variables for BMP performance. This research is intended to build on that
effort by conducting more in-depth evaluations of the design parameters that appear to
affect BMP performance but are not well understood. See section 3.2.7 for a discus-
sion on BMP design variables. The research gaps addressed under this research state-
ment are listed under the Design Variables Affecting BMP Performance section of
Table 4-1.
Research Objectives
· Evaluation of design variables that are related to biochemical and geochemical
treatment mechanisms in BMPs, and
· Implementation of pilot-scale experiments that evaluate the relation of various
design variables to BMP performance.
Tasks
1. Review the Findings of NCHRP 25-20(1) and Select Design Variables: Select one
or two BMP types and design variables, based on the findings of NCHRP 25-20(1),
to further evaluate design versus performance. Prepare a study plan to conduct a
laboratory or field program (preferable), or both, to explore these design variables.
2. Conduct BMP Design Variables Evaluation: Conduct a laboratory or field pro-
gram evaluation, or both, of BMP design parameters. Report on findings in terms
of recommendations for improving designs. Develop recommendations regard-
ing future testing and evaluation efforts.
Estimated Project Budget: $250,000 to $400,000; 2436 months to complete.
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BMP Modeling Tools
BMP modeling tools are important to transportation agencies, particularly when
highway runoff is draining into sensitive receiving waters. Increased understanding of
BMP performance, the factors and designs that affect performance, and how BMPs ulti-
mately affect receiving water quality has increased the need to identify and to improve
BMP modeling capabilities. Several NCHRP projects, as well as other projects, have
resulted in increased understanding of BMP performance. The purpose of this project
is to develop guidance on BMP performance modeling. See section 3.2.10 for a dis-
cussion on BMP modeling. The research gaps addressed under this research statement
are listed under the BMP Modeling section of Table 4-1.
Research Objectives
· Evaluation of state-of-the-art BMP modeling approaches and development of
guidance for model selection, needed model improvements, and application;
· Development of unit treatment models that incorporate sorption, biodegradation
and uptake, photolysis, and volatilization;
· Development of simulation models for BMP treatment trains;
· Implementation of pilot experiments to collect data needed for parameter estima-
tion and model calibration; and
· Development or evaluation of models that can be used for simulating pollution
deposition within BMPs to assess potential impacts to wildlife.
Tasks
1. Review the Findings of NCHRP 25-20(1) and BMP Modeling Research: Evalu-
ate the results of the NCHRP 25-20(01) project to develop unit process descrip-
tions of BMP performance and other relevant BMP modeling papers and to com-
pile a listing or description of potential needs for BMP modeling improvements.
Identify model approaches that may apply faulty logic (such as attributing all pol-
lutant generation to model "build-upwash-off" functions that then result in
faulty street sweeping effectiveness estimates).
2. Review Available BMP Models and Approaches: Review the available models
that typically are employed to model BMP performance and suggest a detailed
list of needed improvements to such models, in order to address the stated research
objectives.
3. Select One Publicly Available Model and Develop Model Improvements: Select
a public domain model, such as SWMM, that typically is used for BMP model-
ing and implement recommended improvements.
4. Develop a Pilot Experiment Plan: Develop a pilot experiment plan to collect the
data needed for the adapted model's parameter estimation and calibration. Develop
a case study and guidance on the model's application.
Estimated Project Budget: $200,000 to $275,000; 1824 months to complete.
Stormwater Detention Hydraulic Performance and Retrofit Options
The hydraulics of stormwater detention systems (ponds and vaults), including wet
ponds and dry extended detention systems and the various combinations of these two
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(including stormwater wetlands) are thought to greatly influence water quality. The
purpose of this proposed research project is to evaluate how the performance of
ponds and other types of detention-based BMPs can be optimized using the careful
consideration and design of hydraulic characteristics of flows routed to and within
these types of BMPs.
Existing transportation infrastructure includes drainage management facilities such
as detention ponds and storm sewers, which must be used, enhanced, and potentially
extended to respond in a cost-effective manner to the increasing requirements of
NPDES, TMDL, and the Endangered Species Act. Practitioners need practical guid-
ance for capturing water quality benefits from BMP infrastructure already in place.
Currently, there are no coordinated programs to address how existing infrastructure can
be modified to benefit water quality. Existing infrastructure removes water from the
roadway, and many hydraulic facilities can be retrofitted to provide water quality ben-
efits; examples include catch basininlet modifications, detention pond retrofit to
embankments and outlet works, riser structures added to culvertembankment systems,
and the fostering of pipe storage in storm drains. The overall potential of retrofit depends
on the incidence of existing drainage systems available and on the receptivity to retro-
fits. See section 3.2.3 for a discussion on hydraulic assessment of BMPs. The research
gaps addressed under this research statement are listed under the Hydraulic Assessment
of BMPs and the Methods to Improve Pollutant Removal in Existing Stormwater Sys-
tems sections of Table 4-1.
Research Objectives
· Evaluation of the characteristics and effects of short-circuiting, bypass, and overflow;
· Evaluation of the nature of correlation between hydraulic residence time and
performance;
· Development of methods or models for estimating the true hydraulic residence in
stormwater ponds;
· Development of methods to optimize detention basin design to maximize treat-
ment; and
· Assessment of retrofit options for flood-control basins and systems that maximize
water quality while maintaining adequate flood-control protection.
Tasks
1. Review the findings of NCHRP 25-20(1) and BMP Modeling Research: Evaluate
the results of 25-20(01) to develop unit processes descriptions of BMP perfor-
mance and other relevant BMP modeling papers and to prepare a review of the
potential characteristics that can be used to optimize performance of detention
systems. Based on this review, develop a detailed study plan for modeling and
field analyses to assess the hydraulic characteristics that lead to improved storm-
water detention BMP design.
2. Develop and Apply Models for Residence Times: Develop or adapt available mod-
els to evaluate the effects of short-circuiting and the relationship between resi-
dence time and performance. Apply models that evaluate the effects of by-pass
and overflow on overall performance on a regional basis. This evaluation will
examine the effects of larger detention sizes versus performance and will include
an assessment of the trade-offs between longer residence times and increased
by-pass or overflow, or both. The results of the task will create a report on how
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short-circuiting can be minimized in ponds via optimization of pond design and
on sizing and drain times versus overall water quality performance. Based on the
modeling work, develop a relationship between pond design factors and hydraulic
residence times for use in design work.
3. Evaluate How Existing Flood-Control Systems May Be Altered to Improve Water
Quality: The purpose of this task is to develop an approach that evaluates sys-
tematically existing flood-control facilities for the feasibility of retrofits to improve
water quality. Identify elements of typical existing hydraulic facilities that may
be modified or enhanced to provide water quality benefits. Review operation and
design principles that can enable feasible and cost-effective modifications--hard
design, extension of the treatment train, and management change. Find and eval-
uate existing retrofits of detention facilities reported in the literature and report
on their cost-effectiveness. Develop water quality retrofit conceptual designs to
enhance water quality elements for as many drainage element types as possible--
detention systems are the primary focus, but also include storm sewers, roadside
channels, trenches, and drainage swales. An assessment of the potential to reduce
flood protection, based on long-term simulations of flooding versus design, should
be made to determine if some systems may be overdesigned and, therefore,
whether some detention volume may be available for water quality improvement.
4. Develop a Guidance Manual: Develop a practical guidance manual for trans-
portation practitioners to select, design, and implement water quality retrofits for
existing highway drainage systems.
Estimated Project Budget: $225,000 to $275,000; 18 months to complete.
Assessment of the Effects of Hydromodification, Sedimentation,
and Turbidity
Changes in runoff volumes due to increased impervious surface from development
have been receiving increasing attention for effects on downstream erosion, sedimen-
tation, and turbidity. Sedimentation and turbidity from the highway runoff can be an
issue, particularly in areas where sanding is employed. Highway construction sites can
be a source of sediments and particulates during the construction phase. The purpose
of this project is to assess the potential for highway sites to contribute to these prob-
lems and to examine how they can impact receiving systems. The project also would
evaluate and produce recommended methods for reducing sources of turbidity and sed-
iments and would attempt to describe where vegetated swales may treat or reduce ade-
quately runoff from highways. See section 3.5.3 for a discussion on sedimentation and
turbidity. The research gaps addressed under this research statement are listed under
the Sedimentation and Turbidity Impacts section of Table 4-1.
Research Objectives
· Examination of the effects of frequent short-term pulses of suspended sediment;
· Identification of additional research needs on the correlation between particle size,
shape, and composition of sediments to fish sensitivity;
· Evaluation of the relationships between seasonal timing and the effect of sedi-
ment load;
· Evaluation of how the knowledge of fish survival responses to turbid water flows can
be applied to the development of mixing zones, work windows, treatment systems,
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and buffers that will allow fish to perform their necessary life functions during
project construction and operation;
· Identification of practical means of controlling turbidity; and
· Development of hydromodification measures (estimated downstream hydrologi-
cal changes) from highway runoff and, subsequently, development of measures for
assessing potential downstream channel and bank instability.
Tasks
1. Prepare a Review of How Sedimentation, Turbidity, and Hydromodification Can
Affect Receiving Waters: Conduct a literature review on the potential impacts
of sedimentation, turbidity, and hydromodification on receiving waters, with an
emphasis on highway runoff. Include a characterization and evaluation of parti-
cle sizes, shapes, and composition from construction sites as well as from com-
pleted highways for different drainage system configurations. Make recommen-
dations for data gathering on needed information.
2. Conduct a Hydromodification Assessment: Using long-term simulation models,
perform an assessment of the conditions under which highway runoff (e.g., high-
way area as compared to watershed area of receiving waters, soils, drainage sys-
tem types, BMP effects, climate, etc.) might either cause or contribute signifi-
cantly to downstream erosion and sedimentation issues. Estimate where a
highway contribution might be negligible as compared to other watershed sources
of runoff and where vegetated swales may treat or reduce adequately runoff from
highways. Prepare guidance on how to conduct more local assessments.
3. Develop Guidance on Minimizing Impacts on Receiving Systems from Turbidity
and Sedimentation: Make recommendations on the relationships between sea-
sonal timing and effect of sediment load for various geographic regions targeted
to important species. Include recommendations on the development of mixing
zones, work windows, treatment systems, and buffers that will allow fish to per-
form their necessary life functions during project construction and operation.
Identify practical means of controlling turbidity to reduce impacts.
Estimated Project Budget: $125,000 to $175,000; 18 months to complete.
Methods to Improve Performance of BMPs
The need for potential enhancements to existing BMPs as well as potential additions
to the design of new BMPs has been identified as a research need. For example, although
BMPs have been shown to be able to achieve certain levels of phosphorus in their efflu-
ent, sometimes there is a need to achieve lower levels. This research project is designed
to explore potential enhancements to BMPs to improve their performance through such
methods as passive chemical additions, real-time chemical additions, and improving and
maintaining the ability to infiltrate while protecting groundwater and other enhancements.
See section 3.2.5 for a discussion on methods to improve pollutant removal in BMPs. The
research gaps addressed under this research statement are listed under the Methods to
Improve Pollutant Removal in Existing Stormwater Systems section of Table 4-1.
Research Objectives
· Development of soil amendment recommendations for use in BMPs to passively
improve performance;
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· Development of methods for improving or maintaining hydraulic conductivity of
infiltration-based stormwater control facilities;
· Evaluation of the effectiveness of sedimentation, filtration, and chemical addition
combinations for stormwater BMP construction projects;
· Evaluation of the potential impacts of coagulants on receiving waters;
· Detailed guidance for areas that require coagulant use to meet water quality
objectives; and
· Development of new technologies and improvements on existing designs to increase
the removal of high-priority pollutants.
Tasks
1. Review the Findings of NCHRP 25-20(1) and BMP Modeling Research: Evalu-
ate the results of NCHRP 25-20(1) to develop unit process descriptions of BMP
performance and other relevant BMP-modeling papers and review other litera-
ture on BMP enhancement options. Prepare a review of the potential enhance-
ments that could be developed for BMPs, including passive and active chemical
addition, infiltration capabilities maintenance and enhancement, reductions in
human pathogens, and other enhancements to improve the removal of additional
targeted pollutants. Potential factors that should be evaluated for enhancing infil-
tration capabilities may include soil amendments, transitional underground stor-
age areas, check dams, and French drains.
2. Prepare a Recommendations Report: Based on the review in Task 1, prepare a
highway BMP enhancements recommendations report that describes potential
enhancements and how they might be applied to BMPs for highway runoff treat-
ment. The enhancements should focus specifically on improvements to targeted
pollutant types.
3. Develop a Testing Plan for BMP Enhancements: Develop a testing plan to con-
duct field evaluations of highway BMP enhancements based on the recommen-
dations report and Task 1. The testing plan should recommend at least two passive
and two active chemical addition technologies, along with other higher potential
BMP enhancements.
Estimated Project Budget: $125,000 to $150,000; 12 months to complete.
Assessment of Potential Impacts on Biota Using BMPs
That Incorporate Habitat
Concern has been expressed increasingly with regard to BMPs that include significant
habitat components (primarily stormwater wetlands) and whether such BMPs expose
wildlife to captured pollutants. Because there is little data to evaluate whether this is in
fact a problem, many turn to examples of wetlands (e.g., Kesterson Marsh in the Central
Valley of California, an agricultural marsh) where the problems have been created from
other pollution sources to draw conclusions. Consequently, potential impacts may be far
overstated. In addition, some regulatory agencies have mandated that mitigation wetlands
not be used for water quality enhancement. Such restrictions may result in suboptimal use
of water resources as well as cost and environmental effectiveness inefficiencies, since
the option of using larger wetlands to satisfy both requirements of habitat replace-
ment and water quality enhancement would not be available, therefore, resulting in the
employment of potentially less effective BMPs. Finally, good design guidance is needed
for minimizing potential negative impact to biota when BMPs that incorporate habitat
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areas are used. See section 3.5.4 for a discussion on the potential toxicity of highway
runoff and section 3.5.9 for a discussion on wetland impacts. The research gaps
addressed under this research statement are listed under the Toxicity and Bioassessment
and the Wetland Impacts sections of Table 4-1.
Research Objectives
· Critical assessment of available information on the potential for highway runoff
BMPs to cause problems for biota and on what habitat values can be achieved
safely with such systems, and
· Development and implementation of a monitoring plan to assess the potential
impacts on biota and the value of habitat created by highway runoff stormwater
treatment wetlands.
Tasks
1. Conduct a Review of Literature on Impacts on Biota from Use of Highway Runoff
BMPs and Constructed Wetlands in Particular: Conduct a literature review on
impacts on biota from the use of constructed wetlands and other BMPs as appro-
priate. Assess the availability of information on highway runoff BMPs and con-
structed wetlands. Evaluate the available information on the value of wetlands
created by highway runoff as well as those designed specifically to treat highway
runoff. Develop a detailed study plan to assess two wetland systems for the poten-
tial impacts and habitat benefits provided.
2. Conduct a Biological Impacts and Values Study: Conduct a study on the two wet-
lands selected that assesses the risk to the biota using these BMPs as habitat and
foraging areas. Include sampling and reporting on water column, sediment, plant
tissue, and invertebrate tissue pollutant testing in areas near inlets and outlets and
in the middle of systems. Perform an ecological risk assessment on the potential
for such systems to impact wildlife and under what conditions and circumstances.
Assess the biological values provided at these two systems by a comparison with
natural wetlands as well as with unintentionally created wetlands with hydrology
from past highway or urban runoff development. Prepare a report that documents
the results of the study.
3. Develop Guidance: Based on the above tasks, develop guidance on how to design
highway runoff BMPs that protect biota and on how to maximize the habitat value.
Estimated Project Budget: $300,000 to $350,000; 24 months to complete.
Evaluation of BMP Design and Performance with Respect to Particle-Size
Distribution in Stormwater Runoff and Associated Metals
Practitioners need effective ways to confine heavy metal toxins to rights-of-way and
to prevent contamination of offsite waters. Suspended solids may be used as indicators
of overall water quality if correlations can be developed with other parameters. Moni-
toring costs can be reduced if the number of individual analyses can be reduced by cor-
relating water quality to suspended solids concentrations. Improving the accuracy of
measurements and representativeness of samples will increase the confidence in load-
ing calculations and correlations.
Most of the contaminants found along highways are associated with particles of a
wide range of sizes (2 mm), but regulatory requirements and biological
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effects typically center on the dissolved constituents. Particle-associated contaminants
are critical to environmental protection and regulatory compliance because
· Contaminants can move between particle bound and dissolved states (e.g., during
a runoff event or during settling in a detention basin),
· Particle-associated contaminants <0.45 mm are counted operationally as dissolved
but could be removed by efficient coagulation and filtration processes in ways that
dissolved contaminants cannot, and
· Future regulations may target directly sediment quality.
DOTs are faced with the technical challenge of developing or modifying existing BMP
designs, so that they also can effectively capture dissolved-phase heavy metals. Most
BMPs aim to treat runoff by removing particles and their associated contaminant load,
but currently there is little understanding of which particles are retained by particular
BMPs and what conditions favor particle retention. At least a portion of the variability of
BMP performance may be attributed to poor understanding of particle dynamics. This
project will address inconsistencies in the performance evaluation of stormwater runoff
BMPs through less costly and more effective particle monitoring compared with cur-
rent wet flow monitoring techniques. In addition to the proper evaluation of BMPs, the
proposed project has the potential to eliminate most pollutant chemical (dissolved and
particulate) analyses by replacing them with particle concentration-based correlations,
saving DOTs significant analytical costs. See section 3.4.2.1 for a discussion on sus-
pended solids and particle-size distribution. The research gaps addressed under this
research statement are listed under the Unit Treatment Processes and the Runoff Char-
acterization with Independent Variable Correlation sections of Table 4-1.
Research Objectives
· Identification and evaluation of accurate and applicable methods for monitoring
particle-size distribution of suspended sediment concentrations;
· Correlation of heavy metals concentrations to suspended sediment in highway
runoff;
· Evaluation of BMPs performance, according to suspended sediment removal and
changes in particle-size distribution;
· Recommendation of improvements for existing stormwater BMPs to improve sed-
iment capture and retention; and
· Recommendation of future research projects for evaluating the potential to treat
metals concentrations not associated with sediment.
Tasks
1. Develop, Test, and Refine Particle Measurement and Collection Methods: Include
hydrographic measurement of particles (first flush, peak, and end-stage of storm
events), testing and development of online particle-size analysis systems, com-
parison of particle sizing methodologies, and study of the impacts of storage and
detention time on particle coagulation and removal,
2. Test the Efficiency and Variability of Particle Removal in Selected BMPs in the
Field: Determine the particle-size distribution of runoff entering and exiting exist-
ing BMPs (or those under development) to characterize removal efficiencies and
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to determine conditions that degrade removal. The dynamics of the particle wash-
off process during storm events also would be examined as degradation in BMP
performance may be related to fine particle breakthrough that will be detected by
this study.
3. Test Measures to Improve Particle Retention and BMP Performance: Based on
the results of the first two tasks, propose and test corrective actions to improve
BMP performance. A critical result of the year-three activities would be to develop
correlations between particle concentrations and dissolved contaminant concen-
trations, which may be useful in replacing chemical analyses by particle-size
measurements in most (or possibly all) applications.
4. Identify Modifications to Basic Treatment Systems to Improve Their Dissolved Met-
als Removal Capability: Undertake a thorough literature review of available treat-
ment technologies that could be applied to highway runoff for reducing metals lev-
els not associated with particulates. Options to be examined should include, but
not be limited to, carbonate/hydroxide/sulfide precipitation, stone/gravel biofilters,
compost or humic filters, and engineered fabric filters. This task would result in a
list of recommended research projects that focus on dissolved metals removal.
Estimated Project Budget: $250,000 to $350,000; 36 months to complete.
Implications and Impacts of TMDLs on DOTs and Guidance in Responding
The Federal Clean Water Act requires that TMDLs for pollutants of concern are
established for Section 303(d)-listed impaired water bodies. Once TMDLs are estab-
lished, waste load allocations (WLAs), or maximum allowable pollutant loads, from
each identified source are set by the state regulatory agency responsible for issuing
NPDES permits. State DOTs are increasingly being subject to the regulatory require-
ments of NPDES permits, including WLAs, for stormwater discharged from their facil-
ities. The issue of TMDLs is a concern to DOTs because meeting WLAs and numeric
effluent limits may increase significantly the cost of stormwater management. Some
DOTs are ill-prepared to make the paradigm shift that the implementation of TMDLs
requires. In order to comply with newly established NPDES regulatory requirements,
DOT stormwater practitioners need to be able to accurately identify pollutant sources,
estimate loads, and know of methods to reduce those loads if necessary. DOTs also
must be aware fully of the legal and economic implications of TMDL development,
implementation, and enforcement. There appears to be a need to provide guidance spe-
cific to DOTs on the effect that TMDLs will have on DOT stormwater management
activities. To this end, the following research objectives and associated tasks have been
developed for consideration. See section 1.1.1 for an additional discussion of TMDLs.
The research gaps addressed under this research statement are listed under the NCHRP
Panel Recommended Research Needs section of Table 4-1.
Research Objectives
· Identification and evaluation of the impact of TMDLs on DOTs;
· Development of guidance on new and improved BMP technologies for runoff
management in the context of TMDLs;
· Provision of guidance on runoff and BMP monitoring to facilitate compliance with
TMDLs;
· Development of recommendations on the types of effluent limits most appropri-
ate and feasible for DOTs in complying with TMDLs; and
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· Identifications and evaluation of suitable tools for runoff and BMP modeling for
prediction of pollutant loads and BMP performance in relation to TMDLs.
Tasks
1. Literature and Practitioner Survey to Determine the State of the Practice and to
Identify Available Sources of Information: Distribute survey forms to and con-
duct phone interviews with practitioners to document the needs and challenges
facing practitioners with regard to TMDL compliance. The literature review will
provide insights into technologies and management strategies as well as ongoing
research on TMDLs.
2. Evaluate the Use of BMPs and New Management Strategies as a Means of Meet-
ing TMDLs: Evaluate BMPs in the context of TMDL compliance. The result of
this phase will be a short list of BMPs and target pollutants typically regulated by
DOT NPDES permits and strategies for compliance.
3. Synthesize Guidance for Runoff and BMP Monitoring Necessary for Demonstrat-
ing Compliance with TMDL: Evaluate monitoring methods and provide standard-
ized monitoring recommendations that can be used to demonstrate TMDL
compliance.
4. Develop Guidance for Pollutant-Load Modeling and Estimation Techniques for
TMDLs: Examine pollutant-load modeling and estimation techniques and provide
analytical methods to be used as planning tools. Examine and test alternative
methods of demonstrating compliance with TMDLs. Emphasize production of
reliable, reproducible, and defensible modeling results.
5. Develop Guidance or Tools, or Both, for Cost Analysis of TMDL Implementation:
Examine methodologies for estimating the costs that may be incurred through
TMDL implementation and compliance. Results of the DOT stormwater practi-
tioner survey likely would be a major component in this research.
6. Develop a Synthesis of Guidance Methods for TMDL Determination and Imple-
mentation: Combine the results of the first four tasks into a guidance document
that can be used by practitioners for TMDL and WLA determination in addition
to stormwater runoff and BMP modeling and monitoring.
Estimated Project Budget: $120,000 to $150,000; 1012 months to complete.
