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57 CHAPTER 3 REVIEW OF PUBLISHED LITERATURE AND POTENTIAL RESEARCH NEEDS As mentioned previously in section 1.4, Research Method- Volume II--Project Documentation, FHWA-EP-03-055; ology, more than 900 of the most relevant annotated cita- and tions from the 2,500-plus documents incorporated into the Volume III--Availability and Documentation of Pub- research database were reviewed, and nearly 300 full docu- lished Information for Synthesis of Regional or National ments were obtained. During the review process, citations Highway-Runoff Quality Data, FHWA-EP-03-056. were categorized according to the following broad research areas: Evaluation of Stormwater Control Facilities and Pro- Volume I is a compilation of "expert chapters" designed grams, Watershed-Based Approaches, Highway Runoff Char- to address different technical issues for monitoring highway acterization and Assessment, and Receiving Waters Impact runoff and urban stormwater. Volume II provides an over- Assessment. After a brief review of some of the major syn- view of the bibliographic database design, the project, the theses of highway runoff/urban stormwater quality research, catalog of available information, the efforts to evaluate avail- each of these subsections and subcategories are discussed. able information, the project quality-assurance and quality- Instead of including a discussion of every document in the control (QA/QC) program, and the directory structure and review, only a selected subset of the most comprehensive files on a CD-ROM accompanying the volume. Volume III documents (i.e., results either were included in the abstract, is a report describing the NDAMS reportreview process and or the full document was acquired successfully, or both) have summarizes and interprets the results of the metadata review been summarized. Nonetheless, all of the categorized docu- process. As a product of this synthesis, a bibliography of ments were considered in identifying potential research gaps more than 2,600 relevant references with more than 1,300 and needs. selected abstracts (or previa--an abstract written by some- one other than then author) and 252 reviewed and classified references were compiled and are available as an online 3.1. BRIEF REVIEW OF RECENT MAJOR searchable database (http://ma.water.usgs.gov/FHWA/biblio/ SYNTHESES OF HIGHWAY RUNOFF/URBAN STORMWATER default.htm). QUALITY RESEARCH NDAMS noted that FHWA, USGS, the Environmental Protection Agency (EPA), and many state highway depart- Several researchers have attempted to compile and sum- ments and universities have sponsored or conducted research marize highway runoff/urban stormwater quality research and on the nature and impacts of highway runoff on water qual- data, including BMP evaluation studies and performance ity, but a centrally available composite of these data was still data. A few of the most notable efforts are described below. lacking, and the existing data present conflicting information. Existing data and studies from FHWA, USGS, state depart- ments of transportation (DOTs), and other sources were com- 3.1.1. National Highway Runoff Water-Quality Data and Methodology Synthesis piled and evaluated to determine whether the information needs of highway managers, practitioners, and researchers are The National Highway Runoff Data and Methodology Syn- being met and whether this information will meet future needs. thesis (NDAMS) is an effort by the U.S. Geological Survey The primary goal of the effort was to determine whether the (USGS) and FHWA to compile and readily make available quality of highway runoff and processes contributing to highway runoff research and guidance information. Three water quality constituents in highway runoff could be char- volumes were published recently (July 2003) as a result of acterized adequately nationwide, based on published informa- the NDAMS: tion. FHWA sought to check the validity of the existing data and procedures to assess and predict pollutant loadings and Volume I--Technical Issues for Monitoring Highway impacts from highway stormwater runoff as a first step toward Runoff and Urban Stormwater, FHWA-EP-03-054; indicating whether current guidelines for highway runoff

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58 quality are up-to-date and technically supportable. FHWA records present in various tables within the database. Note wanted a catalog of existing studies and available data as well that some of the sites in the database include multiple BMPs as indications of the robustness of the data, the sufficiency of (e.g., filters and detention), and therefore the total number of the data to characterize pollutant loadings and impacts from sites is less than the total number of BMPs. highway and urban stormwater runoff, and the changes in A summary of data stored in design tables and associated atmospheric deposition around the country since the mid- flow and water quality records is provided in Table 3-2. The 1980s. To this end, and to assess the suitability of available event monitoring summary information provided in Table 3-2 data to validate runoff quality models developed by FHWA, does not include grab samples or flow measurements and pre- a catalog of available data and investigations was developed. cipitation data that are not associated with measured or cal- culated event mean concentrations. As demonstrated in Table 3.1.2. International Stormwater BMP Database 3-2, retention ponds are the best-populated BMP category in the current database. At the other extreme, some BMPs have Probably the most widely recognized resource on BMP only a single site (e.g., infiltration trenches) in the database. effectiveness data is the award-winning International Storm- A summary of the geographical distribution of BMPs is water Best Management Practices (BMPs) Database at http:// provided in Table 3-3. Based on analyses of the data stored www.bmpdatabase.org/. The database was known formerly as in the BMP database, the database team has come to the fol- the National ASCE/EPA Stormwater BMP database (the name lowing conclusions with regard to evaluating BMP perfor- of the database was changed to recognize and acknowledge mance (Strecker et al., 2000): data contributors outside of the United States). This database provides access to BMP performance data in a standardized Substantially more data are needed for many BMP format for roughly 200 BMP studies conducted over the past types to be able to explore meaningfully design versus 15 years. This database is intended to provide a consistent, performance. scientifically defensible set of data on BMP designs and related Removal percentages are not very useful for character- performance. The database team has made an extensive effort izing performance, unless looked at much more care- to assess the quality of the data entered for consistency and fully (e.g., with treatability information). As a result, accuracy. However, in compiling such a large set of data, and BMP performance requirements generally should not be because of limits on resources for data QA/QC, the developers specified in terms of percent removal. acknowledge that some data may contain errors. Effluent quality among BMPs of the same type is much The database may be searched on or downloaded from the more consistent then percent removal and is thought to website and also is available on CD-ROM. The database was be a better way of characterizing efficiency; although, at developed by ASCE's Urban Water Resources Research an individual site, it is important to test whether the BMP Council under a cooperative agreement with EPA. In 2003, had a statistically significant effect on water quality. new structural BMP storm event and analysis tables were As effluent quality is fairly consistent, some BMP types added to the data search page. These tables allow for may have been mischaracterized as less effective because parameter-specific searches on all structural BMPs analyzed of cleaner influent. For example, BMPs that rely on set- by the project team. tling as a primary removal mechanism cannot have high A summary of the number of data records currently resid- percent removals where suspended solids concentra- ing in the BMP database is shown in Table 3-1. The database tions are low in the influent. The influent data in the dry- is relational in design, and Table 3-1 describes the number of extended detention ponds in the database are relatively TABLE 3-1 Summary of records found in ASCE/EPA BMP Database (as of August 2002) Category Records in Database General Test Site Information 158 Sites Sponsoring and Testing Agencies 60 Agencies Watershed Information 167 Watersheds Nonstructural BMPs Information 28 BMPs Structural BMPs Information 170 BMPs Monitoring Stations 557 Monitoring Stations Precipitation Data 3,396 Precipitation Events Flow Events Monitored 6,563 Flow Events Monitored Water Quality Sampling Event Data 8,588 Water Quality Events Monitored Water Quality Laboratory Analyses 122,265 Analyses Conducted

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59 TABLE 3-2 Summary of data by structural BMP type (as of August 2002) Number of BMPs Precipitation Water Quality in Category, Flow Records BMPs Type Records for Records for Including Design for BMPs Type1 BMPs Type1 BMPs Type1 Information Detention Basin 24 129 229 4,209 Grass Filter Strip 32 227 385 6,251 Media Filter 30 187 327 6,144 Porous Pavement 5 5 5 55 Retention Pond 33 378 817 14,293 Percolation Trench and Dry 1 3 3 21 Well Wetland Channel and Swale 14 53 113 1,241 Wetland Basin 15 221 681 7,320 Hydrodynamic Devices 16 169 309 6,186 Total 170 1,372 2,869 45,720 1 Only events that included the collection of event mean concentrations have been included in the summary statistics presented in this table. cleaner than other BMPs, and therefore they have been overall runoff volumes; wetland channels and basins do not reported as achieving lower percent removals. In fact have this ability. their effluent quality is relatively close to wet ponds and Even with the expanded database there are still many wetlands. limitations: Long-term trends in receiving water quality, coupled with biological assessments, probably would be a much The data are for storm event means only, making it impos- better gauge of the success of the implementation of sible to do intra-storm processes analyses; although, for BMPs, especially on an area-wide basis. the sites that have included more detailed data, intra- storm data may be available. Some grab samples are Strecker et al. (2003) reanalyzed the data in the currently included in the data sets. expanded database and found that in addition to effluent Source reports of the data must be obtained by contact- quality, BMPs are best described by their ability to reduce ing the project team and requesting a paper copy of the runoff volumes (i.e., how much stormwater can the BMP source information. prevent) and process variable flows (i.e., how much is treated Few cost data are available. by the BMP). Table 3-4 compares the ability of some BMPs The only summary results on the web site are cross- to reduce stormwater runoff volumes. Notice that biofilters sectional performance data for a selected BMP based on and detention basins have the ability to reduce significantly aggregating the individual storm event data for some or runoff volumes, making them effective controls for reducing all of the events. TABLE 3-3 Total number of BMPs by state (as of August 2002) State Number of BMPs State Number of BMPs Alabama 13 North Carolina 6 California 41 Ohio 1 Colorado 4 Oregon 3 Florida 24 Texas 19 Georgia 2 Virginia 29 Illinois 5 Washington 20 Maryland 4 Wisconsin 10 Michigan 5 Other 2 Minnesota 7 Total 198 New Jersey 3

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60 TABLE 3-4 Comparison of average of mean outflow to mean inflow for selected BMP types contained in the BMP Database BMPs Type Mean Monitored Outflow/Mean Monitored Inflow for Events Where Inflow is Greater Than or Equal to 0.2 Watershed Inches Detention Basins 0.70 Biofilters 0.62 Media Filters 1.00 Hydrodynamic Devices 1.00 Wetland Basins 0.95 Retention Ponds 0.93 Wetland Channels 1.00 All of the interpretive results depend on the storm event portation's (Caltrans) Caltrans' New Technology Report. The definition. report, issued twice (with revisions, updates, and new infor- The database is not structured to handle time series data mation) in 2003, consolidates and standardizes information on efficiently. new technologies developed or identified as part of the Cal- Relatively few studies have data on bypass flows versus trans process for BMP identification, evaluation, and approval. those treated. Since 1996, the Caltrans stormwater program has evaluated and approved a wide range of BMPs for use on Caltrans facil- The database research team is actively pursuing new data ities and has approved more than 110 separate BMPs. New sets compatible with its requirements. To facilitate this com- technologies--including the latest innovations in permanent patibility, the site recommends use of Urban Stormwater BMP stormwater treatment and control and the existing technolo- Performance Monitoring: A Guidance Manual for Meeting gies used but not selected (approved) previously as a BMP the National Stormwater BMP Database Requirements, of by municipal or DOT stormwater management programs-- which there have been more than 25,000 downloads to date. are evaluated and described for practitioners in a standard- In addition to the detailed BMP monitoring and data analy- ized format. New technologies are identified from the liter- sis guidance provided in the manual, the guidance manual ature, consultants, manufacturers, regulators, third parties, includes lists of required and recommended data elements, or Caltrans personnel, or through the agency's formal New Prod- metadata, that should be reported with BMP performance uct Review Process. Fact sheets for new technologies sum- data, including specific information for individual BMP marize constituent removal effectiveness and the advantages types. The manual also includes sample BMP metadata forms and constraints of each type of new technology presented in to ensure that all of the necessary data elements are recorded. the report. Many of the new technologies identified are appro- References to other BMP performance guidance manuals are priate for ultra-urban environments. included in Appendix B. Favorable evaluations of promising BMPs often lead to The database team's tasks have not included and will not pilot studies for gathering definitive performance data. So far, include recommendations of one BMP type over another; there have been 121 full-scale and small-scale pilot studies. however, the team does report on the performance charac- Five of the most recent pilot studies addressed low impact teristics of BMPs based on the entered data and information development (LID) areas such as bioretention and constructed in the database. Peer-reviewed performance assessment tech- wetlands, Direct Flow Inclined-Screens Gross Solids Removal niques are included. The database is intended to provide a Devices (GSRD), Forward Sloping Screens GSRD, and data-exchange tool that permits characterization of BMPs Reverse Sloping Screens GSRD. Austin filters with alterna- tive media and infiltration basins with alternative media are based solely on their measured performance using the same being considered for pilot testing. Successfully piloted tech- protocols for measurements and reporting information. nologies may be approved and listed in the statewide man- agement plan (SWMP) as a permanent BMP to be used where 3.1.3. Caltrans' New Technology Report applicable by all Caltrans project engineers as part of signif- icant construction and retrofit projects. One of the best consolidated sources of evaluative infor- Also, fact sheets are developed for each newly identified mation on BMP technologies, and on new and ultra-urban technology that is not approved as a BMP by Caltrans. Each BMPs in particular, is the California Department of Trans- fact sheet presents summary information to be used by Cal-

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61 trans Soil Water Assessment Tool (SWAT) members to water runoff; with more consistent effluent quality from evaluate the potential applicability, as well as specific advan- BMPs, percent removal becomes a function of how tages and constraints, of a given BMP to various DOT facil- polluted the inflow is. ities, including for design parameters, operations, mainte- To ensure that data of the highest quality are pro- nance, treatment effectiveness, and costs. All fact sheets use duced, storm event monitoring requires that samples be a standard format to facilitate comparison among various collected according to standard protocols. The criteria BMP types. Each fact sheet is divided into a standard series applied for defining the confidence level were of discussion topics. High: The information came either from a Caltrans These topics, and the relevant information included under research study or from a study that met the Caltrans each topic, are discussed below. QA/QC monitoring protocols. Medium: Constituent removal rates were established 1. BMP Description. A description of the BMP is pre- from the results of a scientific monitoring study or sented at the top of each fact sheet. The description pro- studies conducted independently of equipment man- vides a summary of the BMP configuration and a gen- ufacturers, and the BMP technology has a docu- eral overview of the treatment process, how the BMP mented history of application for treating stormwater; operates, and considerations that need to be addressed or the treatment process was a known technology for for promoting maximum treatment effectiveness and treating other types of wastewater discharges; or the functionality. BMP technology provided no discharge to surface 2. Constituent Removal. The relative degree each BMP is waters under design conditions. Constituent removal able to remove selected groups of constituents from was assumed to be 100% removal, although it was stormwater runoff is provided. The groups of constituents recognized that certain large storm events would not examined were selected based on the likelihood of occur- receive treatment. rence at transportation facilities at levels that would Low: The BMP monitoring program used to quantify require treatment consideration. For each of the selected the removal percentages and the applied monitoring constituent groups [total suspended solids (TSS), TDS, protocols could not be substantiated. total metals and dissolved metals, pathogens/BOD, nutri- 3. Caltrans SWMP Category. Caltrans has developed ents, litter, and pesticides], a level of confidence in the the following categories for BMPs: available data and a general assessment of the BMP's Category I BMPs: Technology-based pollution pre- ability to remove various categories of pollutants are vention BMPs to meet the maximum extent practi- provided. The fact sheets report relative removal effi- cable (MEP) requirements for designing and main- ciencies (high, medium, or low) for each of the nine taining roadways and related facilities; general categories of constituents, derived from the lit- Group A: The BMPs applicable to all maintenance erature review. Constituent removal was quantified by operations, and first calculating the average removal percentage for all Group B: The BMPs used in the design of new constituents within a given category (sediment, nutri- facilities or major renovations of existing facilities. ents, pesticides, metals, pathogens, and litter) and then Category II BMPs: Controls to meet BCT/BAT defined using the following criteria: requirements for construction projects; and High: average removal percentage was equal to or Category III BMPs: Treatment BMPs to meet MEP greater than 75%, requirements. Medium: average removal percentage was between 4. Key Design Elements. Elements that have been high- 40 and 75%, or lighted by vendors in the literature or as a result of test- Low: average removal percentage was less than or ing. Ancillary facilities assumed to be used in conjunc- equal to 40%. tion with the new technology also are listed in this The fact sheets provide notes with additional infor- section. An example would be including a detention mation regarding how the removal assessment was basin downstream of a chemical treatment technology assigned to a given BMP. to capture flocculated particles. A caveat is that the level of confidence in the con- 5. Schematic Figure. If appropriate, a schematic figure stituent removal data found in the literature depended is provided to depict graphically a typical design plan on the type and amount of information. Assessing con- or cross-section, or both, with the major components stituent removal from stormwater BMPs is not a precise identified. science. In fact, the National BMP Database project 6. Capital, Operational, and Maintenance Cost Assess- found that percent removals are not an accurate mea- ments. Assessments pertaining to the costs of building, surement of performance (Strecker et al., 2000). Water operating, and maintaining each BMP also are pro- quality monitoring studies have demonstrated the wide vided, with the level of confidence in the available data variability in water quality concentrations in storm- and a general assessment of the BMP's overall costs.

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62 The level of confidence in the costs to build and oper- Staffing/Equipment: identifies the level of staff, and ate a BMP depends on the type and amount of infor- their skills, required to perform the maintenance, as mation found in the literature. Using the cost informa- well as any specialty equipment. tion developed for municipal stormwater programs was For the project development category, the topics include not considered by Caltrans to be directly relevant to Right-of-Way Requirements: identifies relative space Caltrans facilities. The right-of-way costs and con- requirements to install the BMP; struction costs of major highway transportation proj- Siting Constraints: identifies siting considerations and ects are typically much greater than the typical sub- limitations, such as soil types, slope of the land, dis- urban street or arterial road that might be constructed tance from existing infrastructure or other natural by a municipal public works department. Furthermore, features, and regulatory requirements; operations and maintenance costs of facilities along Design Complexity: identifies major components and major freeways can be much more expensive than simi- equipment requirements and operational controls or lar municipal facilities because of limited access and the limits; and need to provide traffic control. The criteria applied for Retrofit Potential: identifies the potential for retro- defining the confidence level of the cost estimates were fitting existing Caltrans facilities. High: Unit cost information was available from a 8. BMP-Specific Advantages and Constraints. BMP- facility designed and constructed by Caltrans or a sim- specific advantages and constraints lists additional ilar state transportation department. advantages and constraints of the BMP that were not Medium: Cost information was available from sev- covered in the previous sections, including hydrologic eral similar facilities constructed under municipal characteristics and regionally specific weather condi- stormwater programs. tions, experiences from actual installations, and expan- Low: No cost information was available from a sim- sion of particular points discussed in previous sections ilar BMP facility that could be verified independently. of the fact sheet. Construction costs were extrapolated from available 9. Sources of Information. Sources of information are pricing information. provided when appropriate (e.g., vendor contact infor- The cost-effectiveness for each BMP was assessed in mation is provided for proprietary technologies). terms of its equivalent uniform annual cost (EUAC) relative to a detention basin. A four-quadrant system was used as a tool to rate each BMP. The cost estimates 3.1.4. Urban Wet Weather Flow Literature were defined by first calculating the typical range of from 1996 through 2002 costs for constructing or operating a BMP on a per acre Clark et al. (2003) compiled and organized wet weather basis. The acre represented the drainage area served by flow (WWF) literature reviews that were published origi- the BMP. Operation and maintenance costs based on nally in the annual literature review issues of Water Envi- the BMP's design life were then added. The EUAC for ronment Research from 1996 through 2002. The document a particular BMP was estimated and then compared includes approximately 3,350 references from the 7 years qualitatively to that of a detention basin. If the EUAC alone. Over this 7-year period, the field of urban WWF was higher than a detention basin, it was marked as a research expanded dramatically, in part due to increased higher cost using the quadrant rating key. The benefit interest in the United States due to the Clean Water Act of the BMP was evaluated relative to the performance (CWA) NPDES stormwater permit program and increased of a typical detention basin. If the constituent removal awareness of the seriousness of urban WWFs throughout the was greater than that of a detention basin, the BMP was world. The document is organized according to the following marked as having a greater benefit. primary topic categories: characterization, pollution sources, 7. Issues and Concerns. Issues and concerns presented monitoring and sampling, surface-water impacts, groundwater information to be considered in maintenance and in impact, decision-support systems, regulatory policies and project development, with a standard set of topics in financial aspects, and control and treatment technologies. Each each category facilitating comparisons between vari- section is divided further into subcategories. For instance, ous BMPs. Under the maintenance category, the stan- highway and other roadway runoff is a subcategory of pollu- dard topics include Requirements: summarizes routine maintenance tasks tion sources. required to keep the BMP functional; Nuisance Controls: identifies whether the BMP has 3.1.5. Center for Research in Water Resources: the potential to create odors, breed mosquitoes, or Highway Runoff Literature Review attract pests; Traffic Safety: identifies the level of potential traffic Barrett et al. (1995) conducted a literature review that control during BMP servicing; and evaluated the impact of highway construction and operation