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98 Building on lessons learned in past trading efforts (WERF- native to highway stormwater management. Since market- funded and others) and using EPA draft policy and other trad- driven watershed-based stormwater management approaches ing documents as general guidelines, proposed research should are relatively new, there exists a need for further research advance watershed-based trading by improving the tools to into the practicality of such approaches, particularly for accomplish trading and by providing guidance for their use. application to highway runoff management. Once completed, Research will develop generic infrastructure tools to assist the current study funded by WERF should provide informa- with trading implementation. Even in places where trading has tion and guidance on how a market-driven, watershed man- been identified as a potential solution, setting up successful agement system could be applied to the highway environment. trading systems is a challenging process subject to various pit- falls. Successful projects are likely to develop and improve the tools to allow trades to occur and probably will address the fol- 188.8.131.52. Primary References lowing questions related to trading infrastructure: Thurston, H. W., Goddard, H. C., Szlag, D., and B. Lemberg. Con- trolling Stormwater Runoff with Tradeable Allowances for 1. Participatory Tools: How are appropriate stakehold- Impervious Surfaces. Journal of Water Resources Planning and ers and participants identified? Management, Vol. 129, No. 5 (2003) pp. 409418. 2. Marketplace Tools: What is necessary for trading U.S. Environmental Protection Agency. Water Quality Trading markets to work? How are potential traders and their Policy. Office of Water (January 13, 2003). commodities brought together in a functional market- U.S. Environmental Protection Agency. Environomics: A Summary place? How will transactions be made? How can trades of U.S. Effluent Trading and Offset Projects. Office of Water and water quality improvements be tracked and man- (1999). aged? What tools can help meet oversight needs such U.S. Environmental Protection Agency. Draft Framework for Water- as accountability and liability for trades? shed Based Trading. Report No. EPA 800-R-96-001, Office of 3. Regulatory Tools: How might regulatory issues such Water (1996). as NPDES permitting, permit conditions, and discharge reporting, affect the potential market infrastructure? 3.4. HIGHWAY RUNOFF CHARACTERIZATION How could potential regulatory constraints be avoided? AND ASSESSMENT 4. Context: Do the tools differ? Should they differ if the trading programs are established in a pre-TMDL envi- This category refers to the hydrologic and water quality ronment or to help meet an established TMDL? characterization of highway runoff before entering water 5. Scale: What are appropriate scales for successful trad- quality control facilities or receiving streams. The knowl- ing programs? At what point is a system too large to edge gained from characterization monitoring helps DOT handle trading programs to improve water quality? planners and managers understand how to establish storm- water management priorities. For simplicity, the research may focus on tools that work for The research category of highway runoff characterization single-pollutant programs, although ultimate extrapolation to and assessment has been well studied and several general multicredit or multimedia markets is desirable. Consideration characterization studies are readily available in the literature. and integration of the environmental and economic parameters However, this category is broad and the level of detail for any necessary to accomplish trading--parameters such as admin- one study may range from the microscale, such as unit chem- istration and transaction costs--are critical in this research. ical processes, to the macroscale, such as gross pollutant transport. Furthermore, because of the variability and com- plexity of environmental systems, the association or correla- 184.108.40.206. Identification of Research Gaps tion between different physical, biological, and chemical and Needs parameters will require several more decades, if not longer, to fully understand at a satisfactory level. Due to this fact, Of the examples of market-driven trading programs this assessment does not attempt to identify all research gaps, reviewed in the literature, none were found that were specific but rather identifies the gaps where there is a current need for to highways. However, the EPA does support trading for a better understanding for the purposes of improved highway both point and nonpoint source load allocations, so the poten- runoff management. The following paragraphs are organized tial exists for trading of highway runoff pollutants. As high- according to subcategories based on perceived needs of the way runoff is typically higher in many concentrations than transportation and water resources community. other urban and nonurban runoff, the potential exists to overtreat highway runoff relative to offsite other nonpoint sources (with some appropriate compensation). As the imper- 3.4.1. General Constituent Characterization viousness of highway facilities can be estimated readily, the excess stormwater runoff tradable allowances system pro- During the last three decades, researchers throughout the posed by Thurston et al. (2003) is a potentially feasible alter- developed world have conducted highway runoff quality
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99 characterization studies. The primary driver for runoff qual- wetlands), and retention measures (retention basins, ity characterization today is regulatory compliance; how- trenches, and wells). These interim design guidelines ever, characterization also is conducted to identify pollutants were developed through the project team's experience of concern for the development or refinement of stormwater and through a thorough review of available literature. quality management programs. In the United States, federal 6. Pollutant Loadings and Impacts from Highway Storm- and state agencies have conducted several studies to identify water Runoff--Published in 1990, this is a culmination the type and range of concentrations of water quality con- of analytical effort using the results of previous water stituents typically found in highway runoff. quality studies in concert with hydraulic, environmen- During the 1970s and 1980s, FHWA funded several stud- tal, and related concerns. The results of this study ies pertaining to highway runoff quality characterization. include a probabilistic design procedure for estimating The following excerpt from Bank et al. (1995) summarizes impacts to waters receiving highway stormwater runoff. the multivolume research reports concerning highway runoff The procedure used and expanded on the predictive quality developed by FHWA: model developed in the first series of reports. Addi- tional runoff water quality data collected by this and 1. Constituents of Highway Runoff--This six-volume other studies subsequent to the original work in the first report, completed in 1981, developed a predictive pro- phase were used to refine the regression analyses sup- cedure for determining the pollutant characteristics of porting the predictive procedure. stormwater draining from roadway surfaces. The pro- cedure is composed of equations that predict the run- The 1990 effort was undertaken to improve the highway off volumes and pollutant wash-off coefficients of practitioner's ability to address highway stormwater runoff 17 water quality parameters for three types of highways. issues. Formulated by Driscoll and others, the model used 2. Sources and Migration of Highway Runoff Pollutants-- factors such as storm event statistics and probability distri- This four-volume report, completed in 1984, identifies bution of site event mean concentration to estimate runoff vol- the sources of potential water pollutants, their deposi- umes, concentrations, and loads, and probability distribution tion and accumulation within the highway facility, and of streamflow to estimate potential dilution in receiving their subsequent removal to the surrounding environ- waters. This statistical model, useful for planners and high- ment. The purpose of this research was to develop way practitioners, uses readily available rainfall statistics and methods for controlling pollutant sources and mitiga- water quality data to produce a frequency distribution of con- tion measures to lessen pollutant levels entering receiv- centration, loads, and effects for receiving waters. ing waters. The existing FHWA model was formulated using data from 3. Effect of Highway Runoff on Receiving Waters--Com- 993 separate highway runoff events at 31 sites in 11 states dur- pleted in 1985, this five-volume report analyzes the ing the period from 1975 to 1985. In the past 20 years, auto- effects of highway stormwater runoff on receiving mobile construction materials, technology, and fuel additives waters. Included in the effort were 1-year field studies at have changed, and these factors have affected the loads from three sites and preparation of three user-oriented manu- highway surfaces. Research has indicated that lead may be als that provide guidelines for collecting information to substantially lower than in the 1970s and 1980s because of use in highway project environmental assessments. 4. Highway Maintenance Impacts to Water Quality--This improvements in fuel formulations, emissions controls, and tire four-volume series of reports, completed in 1985, sum- wear (even though total vehicle miles traveled has increased). marizes a research project involving impacts from high- FHWA has a study underway with USGS to incorporate way maintenance practices on water quality. Research the existing model in a new user-friendly software platform; efforts included (1) evaluating the impact potential of update the existing model with new streamflow and rainfall routine practices; (2) developing assessment methods data; and expand the model to include the availability of dis- for specific practices; (3) identifying measures to miti- solved concentrations, sediment size information, sediment- gate impacts; and (4) conducting field studies to better chemistry information, and a data quality advisory system. define impacts from two common practices, herbicide The final version will be an updated version of the existing application and surface treatment (seal-coating). 1990 model, along with a new version of the model that is 5. Retention, Detention, and Overland Flow for Pollu- designed to incorporate new highway runoff data as it becomes tant Removal from Highway Stormwater Runoff-- available. This information will benefit the municipalities This report, completed in 1987, provides interim guide- and state and federal agencies charged with estimating high- lines for the removal of pollutants from highway way runoff pollutant loads. stormwater runoff. Three general types of management In addition to the FHWA-funded research, several other measures have been determined, through previous highway runoff characterization studies have been conducted FHWA studies, to be effective in treating highway by state DOTs and independent researchers. Stormwater sam- runoff: vegetative controls (overland flow and grassed ples collected by the Michigan DOT at three major highways channels), detention basins (wet detention basins and indicated that concentrations of conventional constituents--
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100 such as biochemical oxygen demand (BOD), TSS, and phos- and summarizes significant findings. Studies related to high- phorus--are comparable to the concentrations collected in the ways are emphasized when possible. The review included FHWA studies of the 1970s and 1980s (CH2MHill, 1998). 44 articles and reports that focused primarily on SVOCs and However, concentrations of metals, lead in particular, were VOCs. Only 17 of these publications are related to highways, lower for the Michigan DOT sampling than they were for the and 5 of these 17 are review papers. SVOCs in urban storm- FHWA studies. This finding can be attributed to the discon- water and sediments from the late 1970s to the mid-1980s tinuation of leaded gasoline and improvements in sampling were the subject of most studies. and analytical techniques. The earlier FHWA data contains Criteria used to evaluate data quality included documenta- only limited information on the dissolved form of metals, a tion of sampling protocols, analytical methods, minimum critical consideration regarding effects of metals on aquatic reporting limit or method detection limit, quality-assurance biota. Therefore, this study fills a significant gap in previous protocols, and quality-control samples. The largest deficiency FHWA highway runoff characterization studies. Organic in documenting data quality was that only 10% of the studies compounds were, for the most part, not detected in Michigan described where the water samples had been collected in the DOT runoff samples. stream cross section. About 80% of SVOCs in runoff are in In a study funded by the Texas DOT, water quality of high- the suspended solids. Because suspended solids can vary sig- way runoff in the Austin area was determined by monitoring nificantly even in narrow channels, concentrations from dis- runoff at three locations on the MoPac expressway, which crete point samples and contaminant loads estimated from represented different daily traffic volumes, surrounding land those samples are questionable without information on sam- uses, and highway drainage system types (Barrett et al., ple location or how well samplers control the quality of sam- 1996). The highest concentrations of all constituents were ples. Comparison of results of different studies and evaluation measured at the high-traffic site [average daily traffic (ADT) of the quality of environmental data, especially for samples >30,000 vehicles]. The concentrations at all sites were simi- with low concentrations, is difficult without this information. lar to median values for similar sites compiled in FHWA's The most significant factor affecting SVOC concentra- nationwide studies of highway runoff quality. tions in water is suspended solids concentration. In sediment, Caltrans has ongoing runoff characterization studies at the most significant factors affecting SVOC concentrations several different types of transportation facilities throughout are organic carbon content and distance from sources such as the state, including highways (congested and free-flowing), highways and power plants. Petroleum hydrocarbons, oil and construction sites, maintenance yards, and park-and-ride sta- grease, and polycyclic aromatic hydrocarbons (PAHs) in tions. Caltrans' Preliminary Report of Discharge Characteri- crankcase oil and vehicle emissions are the major SVOCs zation Studies summarizes runoff quality data collected since detected in highway runoff and urban stormwater. the 20002001 wet season from more than 50 sites (Caltrans, The few loading factors and regression equations that were 2003). With the exception of total dissolved solids, TSS, dis- developed in the 1970s and 1980s have limited use in esti- solved lead, total lead, and dissolved arsenic, all of the mean mating current loads of SVOCs on a national scale. These concentrations from the congested highways were greater factors and equations are based on few data and use incon- than the mean concentrations from free-flowing highways; sistent units, and some are independent of rainfall. Also, however, none of the differences were statistically significant. more cars on the road today have catalytic converters, and For the most part, the data agree with the ranges reported in fuels that were used in 2003 are cleaner than when loading FHWA's studies as well as with studies by Texas DOT and factors and regression equations were developed. Michigan DOT. As with Michigan DOT's study, lead con- centrations were generally less in the Caltrans data as com- Comparisons to water-quality and sediment-quality criteria pared to the FHWA data. and guidelines indicate that PAHs, phenolic compounds, and phthalates in runoff and sediment exceeded EPA drinking- water and aquatic-life standards and guidelines. PAHs in 220.127.116.11. Constituents Specific to stream sediments adjacent to highways have the highest the Highway Environment potential for adverse effects on receiving streams. Few data exist on VOCs in highway runoff. VOCs were Volatile Organic Carbons. Many studies to characterize con- detected in precipitation adjacent to a highway in England, centrations of semivolatile organic compounds (SVOCs) in and chloromethane, toluene, xylenes, 1 2 4-trimethylbenzene, highway runoff and urban stormwater have been conducted and 1 2 3-trichloropropane were detected in runoff from since 1970 (Lopez and Dionne, 1998). To a lesser extent, a highway in Texas. In urban stormwater, gasoline-related studies also have characterized concentrations of volatile compounds were detected in as many as 23% of the samples. organic compounds (VOCs), estimated loads of SVOCs, and Land use could be the most significant factor affecting the assessed potential impacts of these contaminants on receiv- occurrence of VOCs, with the highest concentrations of VOCs ing streams. found in industrial areas; temperature is another factor. Urban This review evaluates the quality of existing data on land surfaces are the primary nonpoint source of VOCs in SVOCs and VOCs in highway runoff and urban stormwater stormwater. However, the atmosphere is a potential source of
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101 hydrophilic VOCs in stormwater, especially during cold sea- (including abrasion effects and hot-temperature chemical reac- sons when partitioning of VOCs from air into water is great- tions with oil fumes), significant release of the PGMs to the est. Tetrachloroethene, dichloromethane, and benzene were environment in the form of fine particles can occur (Carolia the only VOCs detected in stormwater that exceeded EPA et al., 2000). This raises concern, because platinum is a known drinking-water standards. cytotoxin and tends to bioaccumulate. Because air quality regulations require catalytic converters in all new cars, the Polyaromatic Hydrocarbons. PAHs are a group of toxic and amount of PGMs released into the environment each year is carcinogenic compounds rarely included in characterization expected to continue to increase. A study conducted by Rauch studies, but often present in highway runoff due to traffic- et al. (1999) investigated the concentrations of PGMs in road related sources. PAHs represent more than 2000 PAH com- sediment samples in 1984, 1991, and 1999 and found a clearly pounds; only 16 have been placed on the EPA list of priority increasing trend, especially as related to particles smaller pollutants (Pawluk et al., 2002). PAHs are ubiquitous and are than 63 µm. emitted from practically every combustion source. Follow- ing combustion, PAHs enter the atmosphere, rivers, and lakes Gasoline Oxygenates. Methyl tert-butyl ether (MTBE), a through wet deposition or through dry deposition, where they gasoline oxygenate, disperses rapidly in water and is less bio- are washed away by stormwater runoff. Specific traffic-related degradable than common gasoline compounds, such as ben- sources of PAHs include tire wear, asphalt and asphalt coat- zene, toluene, ethylbenzene, and total xylene (BTEX). USGS ings, vehicle exhausts, and lubricating oils and grease (Pawluk sampled stormwater in 16 cities and metropolitan areas that et al., 2002). Other sources include industrial effluents and are required to obtain permits to discharge stormwater from spills or intentional dumping. their municipal storm-sewer system into surface water (Delzer Some PAHs will evaporate from water and soil, but the et al., 1996). Concentrations of 62 VOCs, including MTBE majority of PAHs in stormwater usually are found in partic- and BTEX compounds, were measured in 592 stormwater ulate form. A stormwater runoff study done by Marslek et al. samples collected in these cities and metropolitan areas from (1997) found that the dissolved phase PAHs represented 1991 through 1995. less than 11% of the total concentrations. In another study, MTBE was the seventh most frequently detected VOC in Shinya et al. (2000) found that the higher molecular weight urban stormwater, following toluene, total xylene, chloro- PAHs were more associated with suspended solids in the form, total trimethylbenzene, tetrachloroethene, and naph- runoff and the predominant PAHs (phenanthrene, fluoran- thalene. MTBE was detected in 6.9% (41 of 592) of storm- thene and pyrene) comprised about 50% of 15 quantified PAH constituents in each sample. In results from Ames' water samples collected. When detected, concentrations of assay, mutagenicity was associated appreciably with PAHs MTBE ranged from 0.2 to 8.7 µg/L, with a median of 1.5 µg/L. in the particulate fraction of runoff water. The dissolved frac- All detections of MTBE were less than the lower limit of tion also showed positive mutagenic response by unknown the EPA draft lifetime health advisory (20 µg/L) for drinking soluble aromatic compounds. Smith et al. (2000) collected 42 water. Eighty-three percent of all detections of MTBE in storm- stormwater runoff samples from four sampling sites (a high- water were in samples collected from October through March way off-ramp, a gas station, and a low- and high-traffic- 19911995, a timeline that corresponds with the expected volume parking lot). For each sample, the suspended-sediment seasonal use of oxygenated gasoline in areas where carbon and water phases were separated and analyzed for 16 PAHs. monoxide exceeds established air-quality standards. The The gas station site produced the highest total PAH loading median concentration of MTBE and benzene for all samples (2.24 g/yr/m2), followed by the high-traffic-volume parking was statistically different and higher in samples collected lot (5.56 × 10-2 g/yr/m2), the highway off-ramp (5.20 × 10-2 during the OctoberMarch season than in samples collected g/yr/m2), and the low-traffic-volume parking lot (3.23 × 10-2 during the AprilSeptember season. Sixty-six percent of all g/yr/m2). In several samples, one or more PAHs were detected MTBE detections occurred with BTEX compounds, and a pro- in the aqueous phase at concentrations above aqueous solu- portionate increase in concentrations was found when these bility. This result suggests the presence of colloidal-size par- compounds occurred together. The proportionate increase ticles capable of sorbing PAHs to an appreciable extent, or could indicate a common source of MTBE and BTEX for the presence of an oil-and-grease microemulsion. those samples. Toluene and total xylene were the most fre- The effects of PAHs on aquatic systems are not well known. quently detected BTEX compounds and the most frequently detected VOCs in these investigations. Detected concentra- Platinum Group Metals. Another group of elements that have tions of toluene and total xylene ranged from 0.2 to 6.6 µg/L been found more recently in urban runoff are the platinum and from 0.2 to 15 µg/L with median concentrations of 0.3 group metals (PGMs): palladium, platinum, and rhodium. and 0.4 µg/L, respectively. PGMs are used in catalytic converters to abate the emission These data raise questions that remain to be answered of aromatic hydrocarbons, CO and NOx. Due to the thermal because these stormwater investigations were not designed and mechanical conditions under which autocatalysts work specifically to characterize the occurrence, sources, and behav-
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102 ior of oxygenated gasoline components in stormwater. Ques- CRWR-263, Center for Research in Water Resources, Bureau of tions include Engineering Research, University of Texas, Austin (1996). Caltrans. Preliminary Report of Discharge Characterization. Report · What are the ranges and seasonal distributions of con- No. CTSW-RT-03-023, (2003). Carolia, S., Alimontia, A., Petruccia, F., Boccaa, B., Krachler, M., centrations of MTBE in stormwater, including munici- Forastierec, F., Sacerdotec, M.T., and S. Mallonec. Assessment pal separate-storm-sewer systems and combined sewer of Exposure to Platinum-Group Metals in Urban Children. Spec- overflows, in other urban areas of the United States? trochimica Acta, Part B, Vol. 56 (2000) pp.12411248. · What is the persistence of MTBE in streams or rivers CH2M Hill. Highway Stormwater Runoff Study. Report, State of that receive stormwater runoff? Are the concentrations Michigan, Department of Transportation (1998). in the receiving stream a cause for concern because of Lopes, T. J., and S. G. Dionne. A Review of Semi-Volatile and Volatile potential effects on aquatic life? Similarly, what effect, Organic Compounds in Highway Runoff and Urban Stormwater. if any, does MTBE have on public water supplies from Open File Report 98-409, U.S. Geological Survey (1998) 67 pp. surface-water sources? Marsalek, J., Brownlee, B., Mayer, T., Lawal, S., and G. A. Larkin. · What proportion of MTBE detected in urban storm- Heavy Metals and PAHs in Stormwater Runoff from the Skyway water is contributed by precipitation and what proportion Bridge, Burlington, Ontario. Water Quality Research Journal of is contributed by overland runoff? How much MTBE Canada, Vol. 32, No. 4 (1997) pp. 815827. Pawluk, D. W., Yonge, D., and M. Barber. Polycyclic Aromatic is contributed to surface water by precipitation that falls Hydrocarbons and Stormwater Management: Past, Present, and directly on larger bodies of water such as reservoirs Future. Washington State University, Department of Civil and and lakes? Environmental Engineering, Seattle (2002). · Do other oxygenates react similarly to MTBE in the Rauch, S., Morrison, G. M., Motelica-Heino, M., and O. Donard. hydrologic cycle and occur in stormwater? Evaluation of Speciation, Transport and Ecological Risk of Pal- · Is land use an important factor in the occurrence of ladium, Platinum and Rhodium in Urban Stormwater Systems. MTBE or BTEX compounds in urban stormwater? Proc., 8th International Conference on Urban Storm Drainage · Is stormwater recharge or precipitation that contains (1999) pp. 202209. VOCs an important source of MTBE to groundwater in Shinya, M., Tsuchinaga, T., Kitano, M., Yamada, Y., and urban environments? M. Ishikawa. Characterization of Heavy Metals and Polycyclic Aromatic Hydrocarbons in Urban Highway Runoff. Water Science and Technology, Vol. 42, No.7-8 (2000) pp. 201208. Smith, J. A., Sievers, M., Huang, S., and S. L. Yu. Occurrence and 18.104.22.168. Identification of Research Needs Phase Distribution of Polycyclic Aromatic Hydrocarbons in Urban Stormwater Runoff. Water Science and Technology, Vol. Many state DOTs have studied highway runoff, so there are 42, No. 3 (2000) pp. 383388. several studies available that generally characterize highway runoff quality. The constituents sampled and the concentra- tions detected do not appear to vary significantly between the 3.4.2. Runoff Characterization with studies; therefore, the research topic of general highway runoff Independent Variable Correlation characterization does not represent a primary research need. However, there is clearly a need for better highway runoff This broad category refers to water quality parameters characterization (including monitoring techniques) of petro- whose presence or magnitudes, or both, are associated with leum hydrocarbons, including PAHs, as well as other trace ele- other parameters or external factors. Correlation often is used ments not normally included in characterization studies, such to account for some of the variability observed in hydrologic as BTEX, MTBE, and PGMs. More advanced highway runoff and water quality data and to build regression equations for characterization studies, such as those that investigate first- predicting difficult-to-measure parameters. Some of the flush phenomena, the correlation of water quality parameters common research questions posed with regard to runoff to independent variables, or the fate and transport of highway water quality correlation include runoff pollutants, will be discussed in following subsections. · How do suspended solids or particle-size distribution relate to constituent concentrations? 22.214.171.124. Primary References · What are the effects of ADT or vehicles during a storm (VDS) on stormwater quality? Bank, F., Kerri, K. D., Young, G. K., and S. Stein. National Evalu- · How do hydrological factors such as the antecedent dry ation of Water Quality Issues for Highway Planning. In Trans- portation Research Record 1483, TRB, National Research Coun- period (ADP), rainfall volume, intensity, or duration cil, Washington, DC (1995) pp. 8991. affect runoff quality? Barrett, M. E., Malina, J. F. Jr., and R. J. Charbeneau. Characteri- · Is there a discernable difference in runoff water quality zation of Highway Runoff in the Austin, Texas, Area. Report No. from different land uses?
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103 126.96.36.199. Suspended Solids and sediment (<63 µm, thus finer than sand) correlates better with Particle-Size Distribution nutrients than does coarse-grained sediment (63 µm), per- haps implying that nutrient transport is more sensitive to the Several researchers have attempted to correlate various movement of fine-grained materials. water quality parameters to suspended solids (the residue Another study reported by Hydro Science (1999) indicates retained on a 1.2 µm filter, also referred to as filterable resi- that 46% of the particulate phosphorus is associated with par- due). Kerri et al. (1985) conducted an intensive runoff mon- ticles that are the size of sand or larger. Phosphorus, with itoring effort at urban highway sites in Redondo Beach, Wal- similar tendencies as heavy metals, also may be bound dis- nut Creek, and Sacramento, California, as well as from a proportionately to larger particles (Glen and Sansalone, 2001). rural site near Placerville, California, in an effort to develop Based on this literature review, it is apparent that a broad and regression equations for estimating pollutant loads from high- clear relationship between particle size and total phosphorus ways. Rainfall and runoff were monitored continuously. Bub- is lacking. Thus, there is a need to characterize suspended bler flow meters were used with automatic sequential samplers sediment loads into fine (clay and silt) versus coarse and to so that stormwater samples could be collected to characterize characterize the nutrients associated with them. entire storm events. The constituents that were analyzed were boron, total lead, total zinc, nitrate (nitrogen), ammonia (nitrogen), total Kjeldahl nitrogen (TKN), total phosphorus, 188.8.131.52. Average Daily Traffic, Vehicles during dissolved orthophosphate, oil and grease, nonfilterable resi- a Storm, and Antecedent Traffic Count due, filterable residue, total cadmium, and chemical oxygen demand (COD). Based on regression analysis, the total resi- Several researchers have attempted to correlate ADT to due (TSS) was evaluated and accepted as a satisfactory inde- loads and concentrations in urban runoff with variable suc- pendent variable for estimating total zinc, nonfilterable resi- cess. Driscoll et al. (1990) found that there was no definitive due, and COD in runoff from highways with average daily relationship between traffic density and pollutant levels. A traffic (ADT) of at least 30,000 vehicles. In another study, strong positive correlation for zinc (r2 = 0.7) and a weak pos- Zhao et al. (1999) correlated suspended solids and COD for itive correlation for VSS, DOC, and TOC were observed. stormwater runoff from an urban highway in Xi'an, China, However, based on the fact that the other metals often asso- indicating that COD is strongly associated with particulate ciated with highway runoff (e.g., copper and lead) did not matter. appear to be correlated with ADT, the authors concluded that Sansalone and Buchberger (1997) studied the association of ADT should not be used as a surrogate measure of pollutant metal elements as a function of particle size for both rainfall levels, and surrounding land use appeared to be more corre- runoff and snowmelt. Solids ranged from smaller than 1 µm to lated to pollutant levels than to ADT. greater than 10,000 µm. Flow rate and duration controlled In a study conducted by Washington State DOT and sum- the yield and size of transported solids. Metal element analy- marized by Thomson et al. (1997), the researchers demon- sis of particle size distribution (PSD) from snow and rainfall strated that storm event loads of copper, lead, zinc, and TKN indicate that zinc, copper, and lead mass increase with decreas- could be correlated with ADT and TSS loads. Correlation ing particle size [i.e., increasing specific surface area (SSA)]. coefficients were all above 0.8, indicating that greater than No clear trends, as a function of increasing SSA or between 80% of the variability of these constituent loads could be snow and rainfall runoff solids, are apparent for cadmium, explained by the variation in ADT and TSS loads. However, which is a very mobile metal and mainly is dissolved in high- single variate correlation of ADT alone was not conducted, way runoff. Based on this study, it is apparent that zinc, lead, so it is not possible to statistically assess the amount of vari- and copper concentrations on solids may vary significantly ability in constituent loads associated with ADT. from one event to another with the tendency for higher con- Table 3-7 is matrix of independent variables that affect var- centrations to be associated with the smaller particle sizes. ious constituent concentrations in highway runoff (Thomson Cadmium concentrations, however, do not tend to vary with et al., 1997). storm events or particle sizes. Kerri et al. (1985) found that the number of VDS was eval- Sediment particle size characterization and its relationship uated and accepted as a satisfactory independent variable at the with nutrient content (especially phosphorus) is an important 5% confidence level for estimating the loads of total lead, total element in the treatability evaluation of stormwater runoff. zinc, filterable residue (TSS), chemical oxygen demand, and Studies from the Lake Tahoe Basin suggest that movement TKN. The authors stress the use of these equations should be of total phosphorus in the tributaries to Lake Tahoe correlates limited to highways with ADT of at least 30,000 vehicles. The with the sediment transport, supporting the contention that numbers of antecedent dry days was found not to be a satis- erosion and nutrient loading are related. However, there factory independent variable for constituent correlation. appear to be conflicting observations suggesting that all sedi- One of the most profound highway runoff correlation stud- ment is not the same with regard to the phosphorus content. A ies found in the literature review was conducted by Irish et al. study by Reuter and Miller (2000) indicates that fine-grained (1995) in Austin, Texas. During this study, 35 storm events
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104 TABLE 3-7 Identification of independent variables affecting constituent concentrations in highway runoff during multiple regression analysis (adapted from Thomson et al., 1997) were simulated using a full-scale rainfall simulator, and eight different pollutants at each of 23 highway sites, con- 23 natural storm events were sampled at the same location; cluded that pollutant event mean concentrations (EMCs) are both events occurred with active traffic. Twenty-one variables independent and unrelated to either rainfall or runoff volume. were identified for each storm event, and multiple regression However, in another study, Colwill (1985) found that the analysis was used to determine the relationship of each vari- amounts of particulate material and associated contaminant able to the quality of the highway runoff. The highway runoff removed from the road surface by individual events are dic- constituents significantly affected by VDS were BOD, lead, tated largely by the intensity of rainfall and the total volume copper, and oil and grease. The highway runoff constituents discharged. Stenstrom et al. (1982) found a strong correlation significantly affected by antecedent dry period traffic count between total rainfall and total mass of oilgrease pollution. (ATC) were COD, BOD, phosphorus, nitrate, and zinc. Therefore, it appears that there is not a significant correlation between runoff volume and concentrations, but there is a sig- nificant correlation between runoff volume and loads, as 184.108.40.206. Hydrological Factors expected. Very few studies were found that investigated the correlation between storm intensity with concentrations or Some of the common hydrological factors believed to loads. However, it is expected that particulate-bound con- affect the quality of highway runoff are ADP and the runoff stituents are influenced greatly by rainfall intensity. volume, intensity, and duration during a storm. As with ADT, researchers have had variable success with the correlation between ADP and stormwater quality. Both Kerri et al. (1985) 220.127.116.11 Land Use Effects and Reinertsen (1981) found that the number of antecedent dry days was not a satisfactory independent variable for con- FHWA and USGS are cooperating on research to deter- stituent correlation. Drapper et al. (2000) and Thomson et al. mine the various components of impervious surfaces to the (1997) found that interevent duration can be a statistically overall stormwater runoff issue using existing land use, land significant factor for pollutant concentrations. Thomson et al. cover, and impervious surface data. There are numerous (1997) showed that iron, TSS, and COD could be positively studies on impervious surfaces, but some have differentiated correlated to ADP. However, other independent variables between rooftops and transportation systems and some have such as storm volume and storm intensity were shown to identified buildings and roads as the only contributor for all account for a greater amount of the variability in concentra- the impervious surfaces. If the components of impervious tions of these constituents. surfaces are broken down into more detailed components With regard to runoff volume, Reinertsen (1981) found that with a watershed, methodologies can be developed and eval- the discharge level alone did not influence the runoff quality uated on how to control and mitigate these impacts. In order as much as might be expected, and in fact no significant cor- to improve understanding of how much each impervious sur- relation was observed between the concentrations and the dis- face is contributing to the total imperviousness for each water- charge either within or between rain events. Driscoll et al. shed, this research specifically examines the percentage of (1990), in their analysis of 184 paired data sets representing transportation infrastructure as well as the percentage of con-
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105 tributions that state transportation agencies maintained high- and rural, congested and free-flowing, total area, percent way systems contribute to the total imperviousness of an urban impervious area, the number of lanes, on- and off-ramps, and watershed. ADT, which has already been discussed. Only a few studies The correlation of land use to pollutant loads has been could be found that discuss differences among some of these investigated by several other researchers over the last few more detailed highway land use classification levels. decades. Probably the largest land use-based runoff charac- Based on their analysis, Driscoll et al. (1990) recom- terization study to date is the EPA Nationwide Urban Runoff mended using urban versus nonurban for classifying high- Program (U.S. EPA, 1983), in which runoff samples were way sites rather than ADT. Caltrans (2003) classified high- collected from 28 major metropolitan areas across the United way sites according to congested and free-flowing, but they States and analyzed over a 5-year period. One of the most have yet to statistically analyze their data. However, after significant findings of this research was that runoff concen- briefly perusing the means and standard deviations of the trations from the various land uses (residential, mixed, com- monitored constituents, it appears that there will not be sta- mercial, industrial, and open/nonurban) were not statistically tistically significant differences between the two classifica- significantly different from one another, with the exception tion types. Thomson et al. (1997) analyzed runoff quality of total phosphorus from open/non-urban land use areas. data from several different highway classification types Regardless of these findings, the characterization of runoff including the total area, total impervious area, and total num- according to land use continues to be a topic of interest for ber of lanes. The analysis revealed that with the addition of many researchers because of the implications for predicting other regression parameters such as TSS, TDS, and TOC, impacts of development. percent impervious area may be useful for predicting COD, Since 1994, the County of Los Angeles has been collecting and the total number of lanes may be useful for predicting stormwater samples from various land uses throughout the chloride, sodium, and COD on a site-specific basis. Drapper county as part of their Phase I NPDES Permit requirements et al. (2000) found that sites incorporating exit lanes have (Los Angeles County Department of Public Works, 2001). recorded higher concentrations of acid-extractable copper Land uses monitored include retail and commercial, vacant, and zinc, supporting the hypothesis that brake pad and tire high-density single-family residential, transportation, light wear caused by rapid deceleration contributes to the concen- industrial, education, multifamily residential, and mixed res- trations of these metals in road runoff. However, these data idential. Results suggest that there are some distinct differ- were discussed qualitatively only. ences in the average runoff concentrations of monitored pol- lutants between land uses; however, the study did not evaluate the statistical significance of those differences. Metals, nutri- 18.104.22.168. Identification of Research Needs ents, and oilgrease concentrations were highest from trans- portation and light industrial and commercial sites, although With regard to suspended sediment and particle size dis- the open space sites had the highest TSS concentrations. tribution, the association of typically observed highway runoff The Oregon Clean Water Agencies published a compila- pollutants with suspended sediment seems to be well charac- tion of land use data collected in Oregon (Willamette Valley) terized. However, there still appears to be a need for better for the Phase I Part II Municipal Stormwater Permit Applica- characterization of constituents associated with different tions that showed that different urban land uses could be char- sized particles in highway runoff, particularly heavy metals, acterized as having different water quality for a number of nutrients, and hydrocarbons. constituents, including heavy metals (Strecker, 1995). Phos- The association of traffic volume with runoff concentra- phorus appeared to be more related to surrounding soil types. tions is well documented in the literature reviewed but still In a study conducted by Stenstrom et al. (1982), five field lacks a statistically valid amount of data to support signifi- sampling stations were selected in a stormwater basin in cant conclusions. ADT does not appear to be a consistently Richmond, California, to determine oilgrease pollution by good predictor of pollutant concentrations and loads. How- land-use type. Samples were taken from the mouth of the ever, VDS may hold promise for estimating concentrations watershed, a parking lot, a commercial street, a residential for some metals and nutrients, as well as TSS, COD, BOD, area, and a light industrial facility. Results of the investiga- and oil and grease. Thus, there appears to be a need for more tion indicated that land use strongly affects oilgrease in research in the area of runoff characterization with correla- stormwater with the major contributing factor being motor tion to VDS. Only one study was found that investigated the vehicles. Areas with the most auto traffic had the highest effects of ATC, so this may also represent a research gap. concentration of oilgrease in stormwater and the highest The hydrological factors such as runoff volume, rainfall hydrocarbon load factor. Mean oilgrease concentration in volume, intensity, and duration are independent variables that runoff flow ranged from 4.13 mg/l in an upstream residential have been shown by a few researchers to affect runoff con- area to 15.25 mg/l in a parking lot. stituent levels. Total storm volume affects loads of some Highways usually are considered an individual land use water quality parameters such as TSS and oil and grease but type but are sometimes further divided according to urban does not appear to significantly affect concentrations. Corre-
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106 lations between intensity and duration with constituent levels Reuter, J. E., and W. W. Miller. Aquatic Resources, Water Quality, are sparse in the literature reviewed, indicating this may be a and Limnology of Lake Tahoe and its Upland Watershed. Chap- research gap. ter 4 of The Lake Tahoe Watershed Assessment, Pacific South- Land use appears to affect average stormwater runoff con- west Research Station, USDA Forest Service (2000). Sansalone, J. J., and S. G. Buchberger. Characterization of Solid centrations, yet no studies have been found that show statis- and Metal Element Distributions in Urban Highway Stormwater. tically significant differences in concentrations based on land Water Science and Technology, Vol. 36, No. 7-8 (1997) pp. use type alone. Land use classification and separation prob- 155160. ably are major factors influencing the variability in land use- Stenstrom, M. N., Silverman, G., and T. A. Bursztynsky. Oil and based runoff concentrations. Land uses often are mixed (which Grease in Stormwater Runoff. University of California-Los Ange- frequently is considered a net benefit to stormwater quality) les' System's Report, Association of Bay Area Governments, making it difficult to classify and to separate stormwater flows. Oakland, CA (February 1982) 241 pp. Differences in classification levels also make it difficult to Strecker, E., Iannelli, M., and B. Wu. Analysis of Oregon Urban compare studies. Runoff quality characterization according Runoff Water Quality Monitoring Data Collected from 1990 to to the various highway classifications, especially urban ver- 1996. Woodward-Clyde (for the Association of Clean Water Agencies) (1997). sus rural, on-ramps and off-ramps, and percent impervious Thomson, N. R., McBean, E. A., and I. B. Mostrenko. Prediction area, appears to be an area needing further research. and Characterization of Highway Stormwater Runoff Quality. Staff at the Center for Watershed Protection, in collabora- Report MAT-94-09, Ontario Ministry of Transportation, Research tion with Dr. Robert Pitt, are compiling and summarizing the and Development Branch (1997). available national data on urban runoff water quality and are U.S. Environmental Protection Agency. Results of the Nationwide conducting data explorations to ascertain potential explaining Urban Runoff Program Executive Summary. NTIS Access number factors. PB 84-185545, Water Planning Division, Washington, DC (1983). Zhao, J. Q., Yu, Y., and W. N. Yuan. Water Quality of Storm Runoff from an Urban Highway. Proc., 8th International Con- 22.214.171.124. Primary References ference on Urban Storm Drainage (1999). Colwill, D. M. Water Quality of Motorway Runoff. Supplemen- tary Report 823, Transport and Road Research Laboratory 3.4.3. Atmospheric Deposition (1985) 26 pp. Drapper, D., Tomlinson, R., and P. Williams. Pollutant Concen- Pollutants in the atmosphere consisting primarily of metals trations in Road Runoff: Southeast Queensland Case Study. and nitrogen can be returned to the earth through processes of Journal of Environmental Engineering, Vol. 126, No. 4 (2000) wet and dry atmospheric deposition. Atmospheric pollutants pp. 313320. are generated from natural and anthropogenic sources. Natural Driscoll, E. D., Shelly, P. E., and E. W. Strecker. Pollutant Load- sources include volcanic activity, windblown dust, forest fires, ings and Impacts from Highway Stormwater Runoff--Volume III. and vegetation. Anthropogenic sources include smelting of Analytical Investigation and Research Report FHWA-RD-88- ores, fugitive dust from emission controls, and automobile 008, FHWA (1990) 150 pp. emissions (Osmond et al., 1995). Wet deposition occurs when Glenn III, G. W., and J. J. Sansalone. Accretion and Partitioning of rain, snow, or fog bring down gaseous or particulate pollutants Heavy Metals Associated with Snow Exposed to Urban Traffic into the atmosphere. Dry deposition occurs when atmospheric and Winter Storm Maintenance Activities--Part II. Journal of pollutants find their way to the earth in the absence of precip- Environmental Engineering, Vol. 128, No. 2 (2001) pp. 167185. Hydro Science. Bioavailable Nutrient Loading into Lake Tahoe and itation (Nilles, 2000). Mercury, lead, and other metals are con- Control Opportunities with an Emphasis on Utilizing SEZs to trolled at the source as required by the provisions of the Clean Treat Urban Runoff. Tahoe Regional Planning Agency (1999). Air Act (CAA), and emissions have been reduced signifi- Irish, L. B., Lesso, W. G., Barrett, M. E., Malina, J. F., and R. J. cantly; however, pollutants deposited previously and atmos- Charbeneau. An Evaluation of the Factors Affecting the Quality pheric nitrogen emitted from various sources--some unregu- of Highway Runoff in the Austin, Texas, Area. Report No. CRWR lated by the CAA--still pose a significant threat to the 264, Bureau of Engineering Research, Center for Research in environment (Osmond et al., 1995). Potential knowledge gaps Water Resources, University of Texas, Austin (1995). in the area of atmospheric deposition include Kerri, K. D., Racin, J. A., and R. B. Howell. Forecasting Pollutant Loads from Highway Runoff. In Transportation Research · Atmospheric pollutant monitoring and sampling meth- Record 1017, TRB, National Research Council, Washington, DC ods and technologies, (1985) pp. 3946. · Modeling and estimation of atmospheric deposition and Los Angeles County Department of Public Works. Los Angeles County 19942000 Integrated Receiving Water Impacts Report. prediction of dispersion patterns, Watershed Management Division (2001). · Characterization of impacts of atmospheric deposition Reinertsen, T. R. Quality of Stormwater Runoff from Streets. Proc., on receiving water systems and biota, and 2nd International Conference on Urban Storm Drainage (1981) · Specific contribution of highways to atmospheric depo- pp. 107115. sition.
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107 Atmospheric deposition can be a significant source of trace Researchers are looking constantly for ways to harness metals. Research performed by Atasi et al. (1998 and 2000) technology for the solution of environmental problems. The attributed cadmium and mercury levels in stormwater runoff use of computer models and the development of new moni- to atmospheric deposition. The objective of the 1998 study toring techniques and equipment is a growing area of atmo- was to investigate the impact of atmospheric deposition on spheric deposition research. Davies (1976) discusses the appli- surface runoff, the combined sewer system, and the publicly cation of remote sensing to highway environmental problems. owned treatment works. Phase I of the study sought to quan- Remote sensing can be used to verify results from computer tify and characterize atmospheric deposition in relation to and mathematical models. It also can reveal the nature and stormwater loadings. Pollutants of interest were mercury, concentrations of pollutant gases and can track the mass flow cadmium, and polychlorinated biphenyl (PCB). A Phase II and transport of pollutants. Davies discusses instrumentation follow-on study may determine the effects of atmospheric and computer models, such as Cospec and Gaspec, and com- loadings on the Detroit Waste Water Treatment Plant. puter models, including a grid-point model, a fixed-source Monitoring and sampling activities were performed using sulphur dioxide model, and a carbon monoxide model. state-of-the-art air and deposition equipment. Sampling was The pollutants contained in precipitation are acquired from performed at sites located in three distinct geographical areas the atmosphere either through rain-out which occurs within and land use types. For each of the three sites, researchers clouds or washout which occurs as precipitation leaves the monitored precipitation, wind speed and direction, and tem- cloud. Shiba et al. (1999) used numerical simulations and a perature. The study concluded that almost 100% of the cad- mathematical model to investigate the origins of atmospheric mium and 3690% of the PCBs in runoff could be attributed pollution found in stormwater runoff. Researchers provide to deposition. Higher-than-expected mercury and cadmium chemical and mathematical descriptions for the cloud drop- levels were observed in runoff from one site; this observation let acidification process, and they conclude that pollutants was hypothesized to be linked to direct deposition from acquired during cloud formation constitute a significant part vehicular traffic. The study showed that atmospheric deposi- of the pollution process. The MAGICWAND model is used to simulate soil and tion was the main source of the study pollutants. water acidification attributable to atmospheric deposition. The Atasi et al. 2000 study investigated the concentrations Bobba et al. (2000) successfully applied the MAGICWAND of 12 trace metals in the atmosphere, in precipitation, and in model to the Turkey Lake Watershed in central Ontario, runoff. The metals sampled included mercury, cadmium, anti- Canada, to evaluate the effects of atmospheric change and mony, aluminum, arsenic, chromium, copper, manganese, deposition. Shivalingaiah and William (1983) discuss the nickel, lead, vanadium, and zinc. Researchers used specialized use of a multiregression model ATMDST, NEWBLD, and equipment and ultraclean analytical methods to monitor mete- SWMM3 to model the Chedoke Creek catchment in Hamilton. orological parameters as well as pollutant concentrations and ATMDST was developed to simulate the dust fall and provide observed that pollutant concentrations were related to spatial input data for NEWBLD to calculate pollutant accumulation. variations and dependent on land use. The conclusions indi- Researchers compared pollutographs from this approach to cated that atmospheric deposition is a significant source for pollutographs generated from the unmodified SWMM3 algo- trace metals within an urban watershed. rithms. Pollutants modeled in this study are suspended sedi- Other studies also have established atmospheric deposition ments, BOD, total nitrogen, and total phosphorous. as a significant source of pollutants. Tsai et al. (2001) investi- Sharma and McBean (2002) developed an atmospheric dis- gated the contribution of atmospheric deposition to loadings of persion model for the transport of PAHs using two indepen- selected pollutants in the San Francisco estuary. Pollutants dent data sets from Ontario, Canada. The object of the inves- studied included copper, nickel, cadmium, and chromium. tigation was to simulate PAH transport and accumulation in Monitoring was performed from August 1999 through August an urban snow pack. Researchers concluded that dry weather 2000, at three different sites chosen to represent the various deposition is a dominant process in the urban environment. segments of the estuary. The study observed dry deposition Estimates of deposition velocities and washout ratios were fluxes of copper, nickel, cadmium, and chromium at concen- comparable to values obtained in previous investigations. trations of 1100, 600, 22, and 1300 µg/m2/year respectively Researchers have attempted to link atmospheric deposi- and at concentrations of 1200, 420, 110, and 230 ng/L respec- tion to external variables such as land use and surface type. tively in precipitation. Researchers concluded that atmo- Halverson et al. (1982) observed higher concentrations of spheric deposition contributed less than 30% of the loadings metals runoff from highly used areas. Runoff sources used in for copper and nickel in stormwater runoff. Contributions for the study included through-fall and stream flow from an urban cadmium and chromium in stormwater runoff approximate tree, a suburban residential roof and street, a moderately used contributions from effluent discharges. By combining direct shopping center, and a heavily used highway. The authors loads to the estuary and indirect loads through stormwater found that the shopping center and the highway were the pri- runoff, atmospheric deposition may contribute up to three mary sources of metals and sulphates. Cadmium, manganese, times as much loading as effluent discharges to the estuary. and copper were observed in only a few samples at very low
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108 concentrations. Garnaud et al. (1999) selected four sites in regions under various land uses. These measurements the Paris metropolitan area to investigate dry and wet weather will be used to validate and calibrate the estimates pro- deposition in an attempt to better understand metal transport duced in task 1. and metal distributions between dissolved and particulate · Identify the pollutants contributed in significant amounts fractions. Researchers provide a comparison of both dis- by atmospheric deposition on a regional- and land-use solved and particulate atmospheric deposits from four roofs, basis using the results of the first two tasks. three yards, six gullies, and one catchment outlet. The authors · Identify sources of organic and inorganic pollutants using observed medium-range transport of atmospheric pollutants. established "fingerprinting" techniques, including atmo- spheric tracers and elemental ratios. · Refine the initial GIS model to predict the atmospheric 126.96.36.199. Identification of Research Needs pollutant contributions and their relative loads on regional and land use bases. There appears to be a paucity of studies that directly relate highways and transportation systems to atmospheric deposi- tion. Filling this gap would provide a better basis to under- 188.8.131.52. Primary References stand how highway-specific atmospheric deposition and dis- persion of highway-related pollutants affect receiving water Atasi, K. Z., Chen, T., Hufnagel, C., Kaunelis, V., and G. Keeler. quality, receiving water biota, and roadside ecosystems. Atmospheric Deposition and Runoff of Mercury and Trace Metal There is also a need to quantify the contribution of atmos- in an Urban Watershed. Proc., WEFTEC 2000 Conference, Ana- heim, CA (2000) 13 pp. pheric deposition to pollutant concentrations found in high- Atasi, K. Z., Fujita, G., Geoffrey, L. P., Hufnagel, C., Keeler, G., way runoff. Stormwater runoff data collected as part of DOT Graney, J., and T. P. Chen. Impact of Atmospheric Deposition on NPDES monitoring programs have revealed that surface Surface Water Runoff of Mercury, Cadmium and PCBs. Proc., runoff from highways and other DOT facilities contains pol- 71st Water Environment Federation Annual Conference, Orlando, lutants known to be unrelated to transportation activities FL (October 37, 1998). (except as spilled during transport). Most of these pollutants Bobba, G., Jeffries, D. S., and R. G. Semkin. Application of MAGIC- are organic and include chemicals with a wide range of volatil- WAND Model to Turkey Lakes Watershed, Canada, to Predict ity. The contribution of organic and inorganic pollutants Changes in Stream Water Quality due to Atmospheric Deposition from atmospheric deposition likely differs between urban- and Climate Change. 2000 Annual Meeting and International Con- ized and nonurbanized areas. The fraction of pollutants con- ference of the American Institute of Hydrology (November, 2000). Davies, J. H. Remote Sensing of Atmospheric Pollutants to Assess tributed by atmospheric deposition is not known for different Environmental Impact of Highway Projects (Abridgment). In land uses or classes of contaminants. Transportation Research Record 594, TRB, National Research Council, Washington, DC (May 1976) pp. 69. Research Objectives. Further research in atmospheric depo- Garnaud, S., Mouchel, J. M., Chebbo, G., and D. R. Thevenot. sition would enable DOTs to Heavy Metal Concentrations in Dry and Wet Atmospheric Deposits in Paris District: Comparison with Urban Runoff. Sci- · Work with other dischargers to reduce pollutants on a ence of the Total Environment, Vol. 235, No. 1-3 (1999) pp. watershed basis, 235245. · Show that they are not responsible for everything appear- Halverson, H. G., DeWalle, D. R., Sharpe, W. E., and D. L. Wirries. ing in their surface runoff, and Runoff Contaminants from Natural and Manmade Surfaces in a Nonindustrial Urban Area. University of Kentucky Urban Hydrol- · Implement the best management practice on a regional ogy, Hydraulics and Sediment Control Symposia (July 1982) pp. basis to better control the organic and inorganic pollu- 233238. tants of concern. Nilles, M. A. Atmospheric Deposition Program of the U.S. Geo- logical Survey. Fact Sheet FS-112-00, U.S. Geological Survey, The following areas were ranked relatively low by state Washington, DC (December 2000). DOTs but could be considered potential research tasks on a Osmond, D. L., Line, D. E., Gale, J. A., Gannon, R. W., Knott, C. second tier list of research priorities based on gaps in the B., Bartenhagen, K. A., Turner, M. H., Coffey, S. W., Spooner, J., literature: Wells, J., Walker, J. C., Hargrove, L. L., Foster, M. A., Robillard, P. D., and D. W. Lehning. WATERSHEDS: Water, Soil and Hydro- · Create a GIS database of regional atmospheric deposi- Environmental Decision Support System. (1995). Sharma, M., and E. A. McBean. Atmospheric PAH Deposition: tion using existing Air Resources Board ambient moni- Deposition Velocities and Washout Ratios. Journal of Environ- toring data and published deposition velocities (for dry mental Engineering, Vol. 128, No. 2 (February 2002) pp. 186195. deposition) and washout ratios (for precipitation inputs) Shiba, S., Hirata, Y., and S. Yagi. Acid Cloud Droplet Formed By to predict mass inputs to varied watersheds. Condensation of Atmospheric Water Vapor as Pollution Source · Measure atmospheric deposition (both dry deposition of Urban Runoff. Proc., 8th International Conference on Urban and precipitation inputs) of major pollutants in major Storm Drainage (August 1999) pp. 15281535.
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111 to observed pollutographs using the coefficient of efficiency and lead. Other significant conclusions of the study include for each event. the following: (1) acidic rainfall generally is neutralized on Computer models are useful for processing large quanti- contact with paved surfaces, and (2) carbonates and fulvates ties of data and solving complex problems; however, in situ- have a substantial effect on dissolved metal speciation, with ations in which quick estimates of quantities are needed, the tendency to form complexes that are not as bioavailable. equations and formulas suffice. Younkin and Connelly In another speciation study by Morrison et al. (1984) zinc, (1981) developed an equation based on regression analysis of cadmium, lead, and copper stormwater samples collected data from nine stream gages and five watersheds in Pennsyl- from selected urban catchments in England and Sweden were vania. The equation can be used to estimate the increase in sus- analyzed. The study found that zinc and cadmium exhibited pended sediment yield in a stream due to highway construc- a preference for the dissolved phase, whereas lead predomi- tion. The equation relates factors such as soil erodibility, nated in the suspended solid phase. Copper was distributed rainfall, construction phases, and site proximity to stream as equally between both phases. Furthermore, the potentially well as increases in quantity of transported sediment. The toxic forms of the metals in the dissolved phase (electro- equation may find applications in highway location studies, chemically available) and in the particulate phase (exchange- highway development impact assessment, and the design of able) accounted for 63% of the total zinc, 77% of the total sediment control devices. cadmium, 66% of the total lead, and 32% of the total copper. Other researchers have investigated the significance of sed- The biogeochemical processes affecting metal speciation iment particle size in sediment transport processes. Ota et al. in a gullypot system and at stormwater outfalls were investi- (1999) investigated the effects of particle size on sediment gated by Morrison et al. (1989). Ionic lead and copper species transport in sewers. They tested three uniform materials of released from road sediments by acid rain are scavenged by varying sizes and observed that test results were very sensi- dissolved organic material and suspended solids as a result tive to particle size. Transport rates were observed to be high of a rise in pH through the roadgullypot system. Cadmium for finer sand. Coarse material was harder to transport. The tends to remain in the dissolved phase. Bacterial activity and graded material was studied further using two different mate- acid dissolution produce increases in dissolved metal in the rials. Modified Meyer-Peter and Muller bed load functions gullypot liquor, and it is these metals that contribute to the were used to fit sediment transport rate for uniform materials. early storm profile. Metals in basal gullypot sediments are mobilized readily during high-volume, high-intensity storms. The resulting stormwater contains dissolved ionic forms of 184.108.40.206. Speciation of Constituents cadmium and zinc, and lead is adsorbed mainly to suspended solid surfaces. Copper also binds to solids, although approxi- Speciation of heavy metals in aquatic systems plays a key mately 50% is transported by dissolved organic material (mo- role in their transport, chemical reactions, and bioavailabil- lecular weight 10005000). For the separation of directly ity. Physical and chemical forms that may cause significant toxic metal species, anodic stripping voltammetry at polymer- consequences, known as consequential species, must be iden- coated electrodes is preferred. Lead and copper are present tified before the potential environmental impact of the metal respectively as iron/humic colloids and organic complexes, can be assessed adequately, since biotoxicity is dependent on which are not directly toxic to algae. Cadmium is predom- the available species and not the total metal concentration. inantly ionic and inorganically complexed and therefore Yousef et al. (1985) investigated heavy metal speciation in directly toxic to algae. rainfall and highway runoff at two sites in central Florida: at Glenn et al. (2002) examined heavy metal (cadmium, cop- the intersections of Maitland Interchange and I-4 and at US- per, lead, and zinc) partitioning results for a series of rainfall 17-92 and Shingle Creek. Total and dissolved fractions of runoff events and found that aqueous chemistry, such as low cadmium, copper, lead, and zinc were determined in the alkalinity and hardness, and short pavement residence time study. The dissolved metals fractions were further divided (less than 30 minutes) can result in a majority of the heavy according to behavioral differences and bioavailability. Dis- metal mass remaining in solution at the edge of the pave- solved metals were first divided according to labile (reactive) ment. Metals partitioning approaches equilibrium conditions and nonlabile (nonreactive) compounds, then according to only toward the end of the event as heavy metals partition to organic and inorganic, and finally by soluble and colloidal. As entrained solids. dissolved metals do not exist as labile-organic-soluble, there are a total of seven possible speciation classifications. Results indicate that the labile, organic, and colloidal fractions aver- 220.127.116.11. Sorption Processes age 82.0%, 5.3%, and 3.2% for cadmium; 92.9%, 0.3%, and 42.7% for zinc; 60.9%, 22.1%, and 55.6% for lead; and Sorption refers to the removal of a solute (sorbate) from 63.7%, 48.9%, and 69.8% for copper in all water samples the solution phase by the solid phase (sorbent). The two basic tested. Therefore, the authors conclude that zinc and cadmium categories of sorption are adsorption (when the sorbate inter- are more reactive, may exist in ionic forms, and are more acts with the surface of the sorbent) and absorption (when the readily available to biota in natural environments than copper sorbate penetrates the surface of the sorbent).
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112 As a result of sorption of heavy metals onto particulate mat- therefore more toxic to aquatic biota than the particulate ter such as iron and manganese oxyhydroxides or organic mat- phase. In fact, in 1993 the EPA's Office of Water revised its ter, the concentrations of metals in natural waters are com- policy to use dissolved metals concentrations rather than monly far lower than would be predicted from simple min- total recoverable metals concentrations to set and measure eral solubility calculations (Bricker, 1999). As such, sorption compliance with water quality standards. The amended processes often are used in stormwater BMP technologies. National Toxics Rule now includes dissolved metals aquatic One important process responsible for the sorption of life criteria (40 CFR 131). Using dissolved metals instead of cations is ion exchange. The negative charge on soil colloids, total recoverable metals for the purposes of assessing clay, and organic matter on soil surfaces makes ion exchange impacts to aquatic life is a step in the right direction, but one of the most important reactions influencing transport of using dissolved metals alone still does not appear to be an cations in soils (Bricker, 1999). Ion exchange involves the adequate measure of aquatic toxicity. As discussed in the lit- sorption of one or more species of ions accompanied by the erature above, the reactive and ionic portions of dissolved desorption of the previously sorbed species equivalent in metals concentrations are more available to aquatic biota total ionic charge. Soils often have surfaces with a net nega- than the nonreactive and nonionic portions. Therefore, there tive charge because of, for example, isomorphic substitution appears to be a need for better characterization of the of ions in a clay lattice structure. An electrostatic double- bioavailable fraction of dissolved metals, as well as trace layer is formed when the negative surface charge is counter- organics, in highway runoff. balanced by cations, which accumulate on the surface of the Sorption plays an important role in the speciation and bio- particle forming an electrostatic double-layer. This double- availability of pollutants. However, the factors controlling layer provides the ability of the matrix to attract ions and sorption, such as cation exchange capacity and specific sur- eventually to attenuate them. face area, are not investigated often. Highway agencies could Sorption processes usually are thought of as beneficial to benefit from information on the sorption capacity of roadside stormwater quality due to the tendency for pollutants to soils for the purposes of prioritizing retrofits and installations adsorb and settle out with sediments. However, Davies and of treatment control practices. Native soils may have the Bavor (2000) found that the adsorption of thermotolerant capacity to retain pollutants, which would circumvent the need coliforms to fine clay particles (<2 µm) contributed to their for additional treatment controls. Based on this fact, there survival in stormwater treatment systems. Other studies iden- appears to be a general need for more research on the sorp- tified by Bricker (1999) have found that metals and trace tion of pollutants to sediment in highway runoff. organic chemicals also tend to adsorb to fine particulates, with metal concentrations on particulates tending to increase with decreasing particle size (increasing surface area), and 18.104.22.168. Primary References that the suspended particulates in highway runoff contained higher overall metal concentrations than road surface dusts. Ashley, R. M., and J. L. Bertrand-Krajewski. Sewer Sediment Ori- gins and Transport in Small Catchments. Proc., 6th International Conference on Urban Storm Drainage (July 1993) pp. 772777. 22.214.171.124. Identification of Research Gaps Bricker, O. P. An Overview of the Factors Involved in Evaluating and Needs the Geochemical Effects of Highway Runoff on the Environment. Open File Report 98-630, U.S. Geological Survey, Washington, Uncertainty exists in identifying sediment sources and DC (1999) 38 pp. defining transport rates and residence time of sediment in Brush, L. M. Urban Sediment Problems. Proc., 2nd International receiving waters. With respect to sediment transport, there Conference on Urban Storm Drainage (June 1981) pp. 518524. appears to be an abundance of information on sediment trans- Coleman, T. J. A Comparison of the Modeling of Suspended Solids port models. However, there may be a need for more detailed Using SWMM3 Quality Prediction Algorithms with a Model studies of sediment transport mechanics in relation to block- Based on Sediment Transport Theory. Proc., 6th International age of full and partly full conduits in various cross-sections. Conference on Urban Storm Drainage (July 1993) pp. 790795. Comprehensive studies on the effects of soils, topography, Cyterski, M. Hydrology and Sediment Modeling Using the BASINS land use, and various storm hydrographs on sediment yield Non-Point Source Model. 2000 Annual Meeting and International Conference of the American Institute of Hydrology, Research Tri- appear to be limited in number. In addition, the behavior of angle Park, NC (November 2000). sediment at inlets, junctions, and transitions in the drainage Davies, C. M., and H. J. Bavor. The Fate of Stormwater-Associated system may require further study. Good predictive models Bacteria in Constructed Wetland and Water Pollution Control that consider runoffstorm relationships, particularly storm Pond Systems. Journal of Applied Microbiology, Vol. 89, No. 2 scour and redeposition, are unavailable. (2000) pp. 349360. Research on the speciation of pollutants has been primar- Fusillo, T. V., Nieswand, G. H., and T. B. Shelton. Sediment Yields ily on the common metals found in highway runoff, cad- in a Small Watershed Under Suburban Development. University mium, copper, lead, and zinc. It is well documented that the of Kentucky Urban Hydrology, Hydraulics and Sediment Con- dissolved phase of the metals are more bioavailable and trol Symposia (July 1977) pp. 302308.
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113 Glenn, D., Liu, D., and J. Sansalone. Influence of Chemistry, · How do hydrological factors and watershed characteris- Hydrology and Suspended Solids on Partitioning of Heavy Met- tics relate to first flush? als to Particles--Considerations for In-Situ Control of Urban Stormwater Quality. Global Solutions for Urban Drainage, Proc., Several researchers have provided definitions of the first 9th International Conference on Urban Drainage (September flush. Barbosa and Hvitved-Jacobsen (1999) noted that a 813, 2002). storm event exhibits a first flush if the first 50% of the runoff Morrison, G. M. P., Revitt, D. M., and J. B. Ellis. Metal Speciation volume contains greater than 50% of the loads. Deletic (1998) in Separate Stormwater Systems. Proc., 3rd International. Sym- posium on Highway Pollution (1989) pp. 5360. defined the first flush as the pollutant load carried by the first Morrison, G. M. P., Ellis, J. B., Revitt, D. M., Balmer, P., and 20% of the runoff volume. Several other definitions used by G. Svensson. The Physico-Chemical Speciation of Zinc, Cadmium, various researchers were summarized by Ma et al. (2002), Lead and Copper in Urban Stormwater. Proc., 3rd International such as first flush is when at least 80% of the pollutant load is Conference on Urban Storm Drainage, Göteborg (June 1984) pp. emitted in the first 30% of the runoff or simply the first 25% 9891000. of the runoff volume (assuming a mass first flush actually Ota, J. J., Nalluri, C., and G. Perrusquia. Graded Sediment Trans- occurs). Another definition is provided, and actually recom- portThe Influence of Particle Size on Sediment Transport over mended by Ma et al. (2002): first flush is when the slope, or Deposited Loose Beds in Sewers. Proc., 8th International Con- mass first flush ratio, of the normalized cumulative mass ference on Urban Storm Drainage (August 1999) pp. 626634. emission versus the normalized volume is greater than 1. This Schroeter, H. O., and W. E. Watt. Practical Simulation of Sediment is a useful definition, because unlike the other methods it does Transport in Urban Watersheds. University of Kentucky Urban not depend directly on the size of the storm event or on the Hydrology, Hydraulics and Sediment Control Symposia (July total loads discharged. Also, the definition provides metrics 1983) pp. 411420. for first flush magnitude and timing, which can be used to size Younkin, L. M., and G. B. Connelly. Prediction of Storm-Induced Sediment Yield from Highway Construction. In Transportation structural stormwater BMPs based on the fraction of loads Research Record 832, TRB, National Research Council, Wash- desired to be captured and to determine when to take first ington, DC (June 1981). flush grab samples. This method does require that storm event Yousef, Y. A., Harper, H. H., Wiseman, L., and M. Bateman. Con- samples are analyzed before compositing, so the monitoring sequential Species of Heavy Metals. Environmental Research costs associated with first flush characterization are signifi- Report FL-ER-29-85, State of Florida, Department of Trans- cantly greater than for general runoff characterization. portation, Bureau of Environment (1985). A broad range of the pollutants found in stormwater runoff Ziegler, A. D., Giambelluca, T. W., and R. A. Sutherland. Model- will exhibit a first flush depending on the drainage hydrology, ing Road Sediment Transport with KINEROS2. Proc., Soil Ero- pollutant mobility, and pollutant supply. With regard to typi- sion for the 21st Century--An International Symposium, Hon- cal highway pollutants, Barbosa and Hvitved-Jacobsen (1999) olulu, HI (January 35, 2001). observed a first flush effect for TSS, zinc, copper, and lead loads. Smith et al. (2000) noted that PAH concentrations were highest usually during the first flush of stormwater runoff and 3.4.6. First Flush Characterization that they tapered off rapidly as time progressed. Lau et al. (2002) reported COD, oil and grease, dissolved organic car- The tendency for concentrations of stormwater runoff pol- bon, and particulate phase PAHs all exhibited a first flush. lutants to increase rapidly at the onset of a storm and then to Wachter and Herrmann (2002) noted that trace organic pollu- decline slowly is known as the first flush phenomena. First tographs of the particle-bound fraction showed a first flush flush can be caused by the accumulation of surface pollutants effect, while Deletic (1998) observed only slight first flush during dry weather and the subsequent wash-off of those pol- effects for suspended solids and conductivity and no first lutants during wet weather. Thus, the first storm of the wet flush effect for pH or temperature. Therefore, it appears that season usually results in the highest first flush concentrations solid-phase pollutants typically exhibit a first flush effect due to the length of the preceding dry period. This is not depending on whether or not the source is continuous or sub- always the case though; in fact, a discernable first flush period ject to buildup and washoff. is not evident for some watersheds and pollutants. Another Hydrological factors such as rainfall intensity and spatial issue is that higher flushes of pollutants have been observed variability, and watershed characteristics such as watershed later in storm events when rainfall intensities increase or per- size, slope, stream order, and percent imperviousness are all vious areas start contributing to runoff, or both. Furthermore, factors that likely are associated with flush phenomena. Under- there is no clear agreement among stormwater professionals standing how these factors influence the flush of pollutants how the first flush should be defined. This leads to the fol- may circumvent the need for site-by-site first flush characteri- lowing research questions: zation. Lee and Bang (2000) analyzed pollutographs from storm events in nine watersheds in the cities of Taejon and · How can first flush be meaningfully defined? Chongju, Korea, and found that for watersheds less than 100 · What water quality parameters are observed commonly ha with a total imperviousness of 80%, the peak of pollutant in the first flush of highway runoff? concentration preceded that of the flowrate, but for watersheds
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114 greater than 100 ha with a total imperviousness of less than or increased during the storm. Consequently, while pollutant 50%, the peak of pollutant concentration was followed by that loads decreased, toxicity potentially increased. Herricks found of flowrate. similar results in his urban runoff sampling work. Caltrans has completed several first flush studies and a final report. Preliminary findings or conclusions can be sum- marized as follows: 126.96.36.199. Identification of Research Gaps and Needs 1. Preliminary results show the existence of a first flush for some parameters, especially for parameters such as Several researchers have identified a first flush effect dur- oil and grease and COD. For medium-size storms, there ing runoff characterization studies, but nearly all use a dif- is generally 40% of the total mass load in the first 20% ferent definition. The mass first flush ratio used to define first of the runoff volume. In some cases metals show a first flush by Ma et al. (2002) appears to be the most meaningful flush as well. Some parameters, such as the sulfate ion, and does not depend on the time of concentration like other show a last flush. definitions that are based on time from beginning of the 2. Strong correlations exist among many of the water qual- storm. There appears to be a need for the adoption of a stan- ity parameters and metals. Antecedent dry periods in dardized method for defining and identifying first flush phe- some cases show trends (greater contaminant concen- nomena. Also, some parameters appear to exhibit a first flush, trations with larger elapsed time between storms), but while others do not. Therefore, a comprehensive list of high- so far there are insufficient data to show statistically way runoff pollutants that tend to exhibit a first flush may be significant correlations. useful for evaluating receiving waters impacts and the feasi- 3. An extensive database incorporating the results from bility of treating only the first flush part of a storm. all sites is being developed and analyzed. Various First flush toxicity information in conjunction with other hypotheses are being tested, including correlations first flush characterization data can be used to design BMPs among parameters to determine if surrogate parameters that can treat properly the early portion of runoff and bypass are useful. the rest for most small watersheds. The current research effort 4. In most instances, a first flush phenomenon also was did not find any studies that specifically investigated how the observed for the gross pollutant and litter concentra- first flush effect was related to hydrological and watershed tions. However, the gross pollutant and litter mass load- characteristics, indicating a potential research gap with regard ing rates were not highest during the first flush but gen- to first flush characterization and assessment. erally appeared to correlate with the peak flow rate, which is similar to the water quality data. The total lit- ter volume generated appeared to be related to the rel- 188.8.131.52. Primary References ative intensity of the storm event. The litter mass load- ing rates also did not generally decrease across the storm Barbosa, A. E., and T. Hvitved-Jacobsen. Highway Runoff and Potential for Removal of Heavy Metals in an Infiltration Pond in season. Portugal. Science of Total Environment, Vol. 235, No. 1-3 (1999) 5. A procedure and notation is developed for quantifying pp. 151159. mass first flush ratios. The notation allows mass first Deletic, A. First Flush Load of Urban Surface Runoff. Water flushes to be analyzed statistically. Research, Vol. 32, No. 8 (1998) pp. 24622470. 6. The concentrations of PAHs were low, generally at or Lau, S-L., Ma, J-S., Kayhanian, M., and M. K. Stenstrom. First below detection limits in the dissolved phase. Particu- Flush of Organics in Highway Runoff. Proc., 9th International late phase PAHs are reported and show a first flush, Conference on Urban Drainage, Portland, OR (September 813, although there were fewer monitored events. 2002). 7. The concept of collecting a grab sample at the best time Lee, J. H., and K. W. Bang. Characterization of Urban Stormwater to approximate EMC for oil and grease was investigated. Runoff. Water Resources (G.B.), Vol. 34, No. 6 (2000) pp. 17721780. Caltrans also initiated research on the first flush of the parti- Ma, J-S., Khan, S., Li, Y-X., Kim, L-H., Ha, S., Lau, S-L., cle size during the 20022003 monitoring season. See sec- Kayhanian, M., and M. K. Stenstrom. First Flush Phenomena for Highways: How It Can Be Meaningfully Defined. Proc., 9th tion 3.5.4, Toxicity and Bioassessment, for further discus- International Conference on Urban Drainage, Portland, OR sion of toxicity studies. (September 813, 2002). In Portland's stormwater monitoring for the NPDES per- Smith, J. A., Sievers, M., Huang, S., and S. L. Yu. Occurrence and mit application efforts and beyond, interstorms were sam- Phase Distribution of Polycyclic Aromatic Hydrocarbons in pled to explore within storm variability (Strecker, 2003). Urban Stormwater Runoff. Water Science and Technology, Vol. Results generally showed that pollutants associated with 42, No. 3 (2000) pp. 383388. particulates did show a tendency to wash off earlier in storms. Strecker, E. W. City of Portland--NPDES Monitoring Results. Constituents such as dissolved metals either showed no change Personal Communication (2003).
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115 3.4.7. Water Quality Runoff Modeling depend on current storm conditions such as runoff volume and number of vehicles during the storm event (Irish et al. Runoff models can be grouped into the following three 1998). main categories based on the method of analysis used in the A study presented by Kerri et al. (1985) resulted in the model: regression-based models, simulation-based models, development of pollutant load estimation regression equa- and stochastic models. Regression-based models are rela- tions for urban highway sites in Redondo Beach, Walnut tively simple and are sometimes no more complex than sim- Creek, and Sacramento in California. The regression equa- ple equations. Simulation-based models are models that are tions were based on continuous rainfall monitoring data and capable of using historical data to account for temporal vari- sequential water quality sampling data. Contaminants ana- ations in the variables of interest. Stochastic models are mod- lyzed included boron, total lead, total zinc, nitrate-nitrogen, els that are founded on the principles of statistics and proba- ammonia-nitrogen, and TKN. The authors cautioned against bility. Models also can be grouped by the kinds of processes using the regression equations in situations where ADT is that they simulate. Geochemical models are specialized mod- less than 30,000 vehicles. els that are used mostly to simulate unit processes. The areas The Washington State study presented by Chui et al. (1982) of interest and possible knowledge gaps with respect to run- resulted in the development of a pollutant load model for off water quality modeling are as follows: Washington State. The model was based on extensive moni- toring data consisting of 500 storms at nine locations. The · The availability of data, data replacement and updating, model correlates TSS loads, traffic conditions, runoff coeffi- and new data requirements; cients, and land use. Pollutant load estimates for individual · Development of hybrid models to benefit from the advan- storms are determined less accurately by the model, as com- tages of each of the categories; pared to multiple storms over a period of time. · Extension of models to predict loads of a wider range of Examples of simulation models include EPA SWMM, pollutants; and STORM, HSPF, and the FHWA urban Highway Storm Drain- · Simulation of herbicide and pesticide concentrations age Model (Barrett et al., 1995). DeVries and Hromadka and transport processes. (1993) present a comprehensive discussion of runoff water quality models. Models discussed include SWMM, HPSF, The main advantages of regression models are in their rela- QUAL2E, WASP4, AGNPS, and MIKE 11. For each model, tive simplicity. Regression methods also tend to have minimal the authors present a general overview that includes a descrip- data requirements; however, these models are less capable of tion of the model's origins and the applications for which the simulating temporal and spatial variations. The advantages of model was developed. A description of hardware require- simulation models include the ability to simulate the effects ments and directions on how to obtain the model also are of changes and abatement effects by a simple alteration of included. In some cases, the authors also discuss model com- parameters and the provision of temporal and spatial distri- ponents and the kinds of problems for which the model has butions. Simulation models tend to have the most substantial been applied. Guay and Smith (1988) discussed the applica- data requirements, which can be problematic due to the high tion and evaluation of DR3M-II and DR3M-qual. The mod- cost of data collection. Statistical models offer the ability to els were applied to a multiple-dwelling residential catchment produce a distribution instead of the mean concentrations and a commercial catchment in Fresno, California. Calibra- provided by regression-type analysis. Distributions can be tion and verification of errors for dissolved solids, dissolved used then to estimate the probabilities of exceedance of spec- nitrite plus nitrate, total recoverable lead, and suspended ified concentrations. However, statistical models are not as solids ranged from 11% to 54%. capable as simulation models at simulating either the inter- Statistical methods were applied in the analysis of runoff actions of flow and concentrations or the effect of abatement quality in the National Urban Runoff Program (NURP), actions (Barrett et al., 1995). EPA's comprehensive 5-year runoff characterization study A review of literature related to runoff water quality mod- in which runoff samples from 28 metropolitan areas across eling shows that there are numerous studies that developed the United States were collected and analyzed (U.S. EPA, or applied, or both, regression models as tools for runoff 1983). The results of the study suggested that EMCs can be characterization. A study to identify the variables that affect described by lognormal distributions. The statistical method- highway runoff in Austin, Texas, applied regression analysis ology used in the NURP program entailed defining dilution techniques for predicting pollutant loads. The results of the ratios and calculating statistical properties of the resulting study suggested that highway stormwater loading variations instream concentrations from the statistical properties of the during a storm event depend on variables measured during flows and concentrations. Frequency of exceedance of any previous events, the antecedent dry period, and the current target concentration during wet weather was obtainable either storm event. TSS loads were found to depend on the build up through the use of formulas, standard plots of cumulative of pollutants before storms, the characteristics of the storm, probability distributions, or calculations from statistical prop- and the wash-off processes. Oil and grease were found to erties of stream concentrations (Barrett et al., 1995).
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116 An FHWA study presented by Driscoll et al. (1990) also differences in runoff quality among different land use types applied statistical methods as the basis for the development could not be validated statistically. There is, though, still a of a procedure for predicting highway stormwater runoff pol- need for forward-looking data collection efforts that focus lutant loadings. The study also developed methods for esti- more on modern parameters and less on parameters of dimin- mating potential impacts on receiving waters, including ishing importance in highway runoff such as lead. There also guidance for evaluating the performance of mitigation mea- is a need to develop hybrid models that take advantage of sures. A total of 993 individual storm events at 31 highway both stochastic and deterministic methods in order to pro- sites in 11 states were monitored. Barks (1996) discussed duce models that have the benefits of both statistical and the development of statistical methods using site-specific simulation-based models. Adaptation of agricultural models data to adjust values obtained from the use of regional equa- for herbicide and pesticide modeling in the context of highway tions so that more accurate values could be acquired. The runoff management would provide insights into the transport regional regression equations were developed using data from processes of highway pesticides and herbicides. The most a national database and are used to estimate runoff pollutant commonly modeled contaminants are heavy metals, nutri- loads. The method consists of a single adjustment procedure: ents, bacteria, dissolved oxygen, and solids. Existing models a regression of the observed data against the predicted values, need to be extended and enhanced to simulate a wider range a regression of the observed data against the predicted values of contaminants. and additional local independent variables, and a weighted combination of a local regression with regional prediction. Geochemical models are useful for evaluating the 184.108.40.206. Primary References bioavailability and mobility of pollutants. Definitions of four categories of models provided by Bricker (1999) include the Barks, C. S. Adjustment of Regional Regression Equations for following: Urban Storm-Runoff Quality Using At-Site Data. In Transporta- tion Research Record 1523, TRB, National Research Council, Speciation Models--Models used to calculate the parti- Washington, DC (1996) pp. 141146. Barrett, M. E., Zuber, R. D., Collins III, E. R., Malina, J. F. Jr., tioning of an element among different aqueous species Charbeneau, R. J., and G. H. Ward. A Review and Evaluation of and complexes. Examples of speciation models include Literature Pertaining to the Quantity and Control of Pollution WATEQF and WATEQ4F. from Highway Runoff and Construction. CRWR Online Report Mass-Transfer Models--Models used to simulated changes 95-5, (April 1995) 186 pp. in solution chemistry caused by mass-transfer processes. Bricker, O. P. An Overview of the Factors Involved in Evaluating Examples of mass-transfer models are SOLMNEQ.88, the Geochemical Effects of Highway Runoff on the Environment. MINEQL+, MINTEQ (4.00), and PHREEQC. Open-File Report 98-630, U.S. Geological Survey, Washington, Mass-Balance Models--Models used to simulate the net DC (1999) 28 pp. changes in the masses of reactants and products in waters Chui, T. W. D., Mar, B. W., and R. R. Horner. Pollutant Loading along a flow path. An example of a mass-balance model Model for Highway Runoff. ASCE Journal of Environmental is NETPATH. Engineering, Vol. 108, No. EE6 (1982) pp. 11931210. DeVries, J. H., and T. V. Hromadka. Computer Models for Surface Geochemical Mass-Transport Models--Models used to Water. In Handbook of Hydrology, New York, McGraw-Hill simulate hydrodynamic advection and dispersion of dis- (1993) pp. 2139. solved species in porous media as well as to speciate the Driscoll, E. D., Shelley, P. E., and E. W. Strecker. Pollutant Load- aqueous solution and determine geochemical mass trans- ings and Impacts from Highway Stormwater Runoff--Volume I: fer. Examples of geochemical mass-transport models Design Procedure. FHWA Report No. FHWA-RD-88-006, Fed- include CHMTRNS, PHREEQM-2d, and PHREEQC. eral Highway Administration, Office of Research and Develop- ment (1990). The author also includes a discussion of the applications and Guay, J. R., and P. E. Smith. Simulation of Quantity and Quality of limitations of each of the above categories. Storm Runoff for Urban Catchments in Fresno, California. Investigation Report 88-4125, U.S. Geological Survey, Water- Resources Investigations, Washington, DC (1988) 76 pp. 220.127.116.11. Identification of Research Gaps Irish, L. B., Barrett, M. E., Malina, J. F., and R. J. Charbeneau. Use and Needs of Regression Models for Analyzing Highway Stormwater Loads. ASCE Journal of Environmental Engineering, Vol. 124, As with BMP Modeling (section 3.2.10.), water quality No. 10 (October 1998) pp. 987993. Kerri, K. D., Racin, J. A., and R. B. Howell. Forecasting Pollutant modeling is heavily dependent on the availability of data. Loads from Highway Runoff. In Transportation Research Report Therefore, there is a general need for accurate and represen- 1017, TRB, National Research Council, Washington, DC (1985) tative data for parameter estimation and model calibration pp. 3946. and for stochastic models development. The NURP study U.S. Environmental Protection Agency. Results of the Nationwide resulted in the development of a large database of runoff Urban Runoff Program--Volume 1. Final Report WH-554, Water characterization data; however, even with this large data set, Planning Division, Washington, DC (1983) 186 pp.
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117 3.4.8. Highway Construction and the sites (Kayhanian et al., 2001). Results obtained during the Vegetation Maintenance 2-year characterization study indicated that Twelve state DOTs indicated that they have conducted stud- 1. Caltrans construction-site runoff constituent concentra- ies or prepared reports on the design or efficiency of storm- tions detected during this study were less than typical water management measures during construction, although 34 Caltrans and non-Caltrans highway runoff constituent state DOTs have not conducted any studies in this area. concentrations, with the exception of total chromium, Highway construction and maintenance activities have the total nickel, total phosphorus, TSS, and turbidity. potential to impact receiving water systems depending on 2. The concentrations of TSS and turbidity likely are due numerous factors, such as land disturbance area, storm event to the disturbed soils present at most construction sites. timing, topographic and geological characteristics, and con- 3. The origin of the high concentrations of total chromium, struction and maintenance BMPs. Construction activities that total nickel, and total phosphorus concentrations is include grubbing, grading, and excavating may reduce slope unknown. Concentrations of these constituents varied stability and increase erosion, thereby increasing sediment between sites, so it is possible that site-specific soils loads and concentrations to receiving waters. Erosion and sed- and vegetative conditions contributed to the concentra- iment controls were discussed in section 3.2.6, and impacts to tions of these constituents. receiving waters caused by sedimentation and turbidity are 4. A correlation (R-squared values greater than 0.5) was discussed in section 3.5.3. Vegetation maintenance activities observed between TSS runoff concentrations and par- such as roadside herbicide application have the potential to ticulate runoff concentrations of chromium, copper, cause impacts to receiving streams. Several researchers have investigated conditions and activities that may contribute to and zinc, indicating that minimizing particulate matter poor runoff quality from highway construction and vegeta- may reduce total metals concentrations. tion maintenance sites. Common research questions posed include In another Caltrans study (Caltrans, 2002), 120 storm events were monitored at 27 construction sites during four rainy sea- · How can suspended-sediment data be used to make ero- sons beginning in 19981999 and ending in 20012002. One sion control and vegetation maintenance decisions at of the primary purposes of the sampling study was to develop construction sites? a baseline set of construction site stormwater quality con- · How does construction site runoff impact receiving centrations. Sites were selected to represent a wide range of waters? typical Caltrans construction activities, geographic areas, and · How mobile are herbicides applied to highway shoulders? hydrometeorologic conditions, as well as other site-specific · How do roadside vegetation maintenance practices impact conditions. The results were reviewed to compare annual receiving streams? means of individual parameters for the four reporting years. Mean concentrations of total lead, nickel, and zinc varied NCHRP Synthesis 20-5, Topic 33-04, is synthesizing road- over the 4-year period, while mean concentrations of total side vegetation practices for erosion control and stormwater copper, cadmium, and arsenic were relatively consistent over management, along with a variety of other purposes. This the study period. All dissolved metals remained relatively research will be available in early 2004. consistent over the study period except for zinc, which had Barrett et al. (1995a) provides a thorough literature review consistently higher concentrations during the later years. of environmental effects of highway construction that includes With the exception of TKN, nutrient concentrations were rel- more than 30 references of studies conducted in the 1970s atively consistent over the 4-year monitoring period, exclud- and 1980s. A more recent investigation by Barrett et al. (1995b) ing one abnormally high total phosphorus concentration in involved monitoring the impacts to Danz Creek in south- the second year. Measured hardness was relatively consistent western Travis County, Texas, during the construction of a over the 4-year monitoring period, while TSS concentrations new highway. Ten storms were monitored at sites upstream were much higher during the second monitoring year com- and downstream of the highway crossing. The results indi- pared to other monitoring years. Total and dissolved organic cated that the concentration of suspended solids in Danz carbon concentrations were low compared to dissolved and Creek increased at least fivefold during and immediately suspended solids, suggesting that dissolved and suspended after storm events despite the presence of a system of tem- solids are composed primarily of inorganic particulate matter. porary controls (primarily silt fences) and restrictions on the Statistical comparison tests showed a statistically significant use of heavy equipment at the creek crossings. The only other difference in measured runoff concentrations between new monitored parameter that appeared to increase substantially construction and modification facilities and existing facilities was iron, due to high iron content in the site soils. Copper and for dissolved copper, total coliform, dissolved lead, dissolved zinc were shown to increase by 11% and 85%, respectively. nickel, and dissolved zinc, with the concentration of each Fifteen highway construction sites were monitored by Cal- of these constituents being lower at new construction sites. trans to assess the water quality of stormwater runoff from Comparing water quality runoff from northern California
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118 versus southern California sites, the statistical comparison test age of the amount of pesticide applied also varied greatly showed a significant difference for dissolved arsenic, dis- (glyphosate: <1%, oryzalin: 0.15.4%, isoxaben: 0.115.0%, solved chromium, nitrate, nitrite, ammonia, TKN, dissolved transline: 44%, and diuron: 0.64.4%). The high percent load- lead, dissolved nickel, total nickel, TSS, TOC, and DOC, with ing for transline undoubtedly was due to its relatively high the majority of these constituents showing higher concentra- solubility. The results of the study suggest that biofiltration tions in southern California. Statistical comparisons between strips along highway roadsides can significantly attenuate seasons showed a significant difference for dissolved ortho- herbicides in runoff, particularly those with low solubility. phosphate, nitrate, ammonia, oil and grease, diazinon, total A study by Wood (2001) investigated the potential of her- coliform, dissolved zinc, TDS, TSS, pH, and specific conduc- bicides applied to roadsides in the Willamette Valley near tance for one or more seasons compared to other seasons. Still, Colton, Oregon, to migrate to nearby surface waters. The study no consistent pattern was observed. Construction site storm- was divided into two phases. During the first phase (spring water runoff data was compared to Caltrans highway runoff 1999), 0.3-inch-per-hour rainfall events were simulated and data. The statistical comparison showed significantly higher runoff was collected 1 day, 1 week, and 2 weeks after the concentrations in highway runoff for total cadmium, dissolved application of an herbicide compound typical of Oregon DOT copper, dissolved lead, total zinc, and dissolved zinc. TSS and application rates and concentrations. The simulated rainfall hardness were significantly higher in construction site runoff was applied long enough to collect between 13 and 15 liters than highway runoff, while oil and grease and COD were sig- of runoff (between 0.5 and 1.9 hours). The EMC in the runoff nificantly higher in highway runoff. of each of the herbicides (diuron, glyphosate, bromacil, and With regard to highway vegetation management a few stud- sulfometuron-methyl) declined by about 1.5 orders of mag- ies were found that investigated herbicide migration from nitude between the first day after application and the second highway rights-of-way. Powell et al. (1996) conducted a study week after application. The results of the simulated rainfall in Glenn County, California, to assess the concentrations of experiments suggested that a heavy rainstorm occurring soon simazine and diuron (herbicides often applied to highway after herbicide application could generate concentrations in rights-of-way) in runoff from the pavement shoulder at three the runoff leaving the road's shoulder of nearly 1 mg/L gly- highway sites during simulated rainfall events and at two phosate and diuron and concentrations on the order of a few sites during natural rainfall events. hundred µg/L of sulfometuron-methyl. Bromacil was not At the simulated rainfall sites, soil was sampled to a depth measured in this phase. During the second phase (winter of 3 m at the site where no runoff occurred and to a depth of 19992000), concentrations were measured in the runoff 1 m at the other sites. Herbicide was not found below a 0.3 occurring from natural rain events after a single herbicide m-depth at any of the three sites. Of the total 38 samples taken application. Five rainfall events were chosen for the sampling. from the top 0.3 m of soil, 13 contained simazine (maximum Runoff flowing directly from the shoulder remained in the concentration 694 µg/kg, found prior to herbicide application) 110 µg/L range for diuron for all events sampled with con- and 17 contained diuron (maximum concentration 874 µg/kg, centrations decreasing with time. Based on the studies summarized above, it is clear that her- just after rainfall simulation). At one of the natural storm event bicides have the potential to migrate to receiving waters. sites, concentrations ranged from 29 to 337 µg/L simazine and However, what is not clear is whether these herbicides pose from 46 to 2849 µg/L diuron. The largest amounts removed in a significant threat to receiving water biota. A study con- any sampled period were 5.3% of the applied simazine and ducted by Johnson and Hall (2002) evaluated the impacts of 8.4% of the diuron in one 28-hr period. SurflanTM (with the active ingredient oryzalin) on Japanese At the other natural storm event site only simazine was medaka (Oryzias latipes), a standard laboratory organism for applied. Samples were collected from a flume that discharged testing impacts to fish. Results from three distinct assays sup- runoff into a drainage canal. The first runoff sample was port the conclusion that Surflan and oryzalin are endocrine- taken after a total of 100 mm of rain had fallen, and simazine disrupting compounds. But, this study was conducted at much concentration averaged 105 µg/L in 5266 m3 of runoff water higher concentrations than those observed by Huang et al. collected. The greatest mass discharge in any sampled period (2002). Since lowest-observed-adverse-effect-levels for repro- was 155200 m3 of runoff in 20 hr, with an average concen- ductive effects of oryzalin and Surflan were not defined in tration of 83 µg/L simazine. this study, and there appears to be a nonlinear dose-response In another study, Huang et al. (2002) investigated the trans- relationship, this study should be repeated at concentrations port of five different pesticides (glyphosate, oryzalin, isox- more typical of highway runoff concentrations. aben, transline, and diuron) in highway biofiltration strips at two geographically separated sites in northern California. Herbicides were detected in runoff water from both sites after 18.104.22.168. Identification of Research Gaps all storm events. The EMC and loading percentage had large and Needs ranges among different herbicides at the two sampling loca- tions for the past three years (glyphosate: 0.121.5 µg/L, The disturbance of land during highway construction activ- oryzalin: 0.142.4 µg/L, isoxaben: 0.114.4 µg/L, transline: ities significantly increases the potential for sediment trans- 0.57.1 µg/L, diuron: 0.110.2 µg/L). Loadings as a percent- port even with the implementation of erosion control prac-
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119 tices. To evaluate the effectiveness of (or need for) erosion Pertaining to the Quantity and Control of Pollution from High- control practices, suspended sediment is the primary (and way Runoff and Construction. Technical Report No. CRWR 95-5, often the only) parameter monitored during highway con- Center for Research in Water Resources (1995a). struction runoff characterization studies. However, it often is Barrett, M. E., Malina, J. F. Jr., Charbeneau, R. J., and G. H. Ward. Water Quality and Quantity Impacts of Highway Construction not clear in the literature, particularly in abstract summaries, and Operation: Summary and Conclusions. Technical Report whether TSS or SSC are being reported, as these two terms CRWR-266, Center for Research in Water Resources (1995b). often are used interchangeably. As discussed by Bent et al. Bent, G. C., Gray, J. R., Smith, K. P., and G. D. Glysson. A Synop- (2001), these two measures of sediment concentration are not sis of Technical Issues for Monitoring Sediment in Highway and transferable because SSC is a measure of the total mass of Urban Runoff. Open File Report 00-497, U.S. Geological Survey sediment, while TSS is a measure of a subsample of the water- in cooperation with the Federal Highway Administration (2001). sediment mixture. Subsampling may inadvertently preclude Caltrans. Caltrans Construction Sites Runoff Characterization Study larger-sized particles, resulting in an underrepresentation of Monitoring Seasons 19982002. Report CTSW-RT-02-005, the true sediment concentration. Due to the fact that TSS is Stormwater Management Division (2002). reported and used often in the calculation of sediment loads, Huang, X., Fischer, M., White, R., Lu, Y., and T. Young. Field Monitoring and Treatment of Herbicide Runoff from Highway there appears to be a research gap in this area and a need to Roadsides. Workshop on Storm Water Monitoring Techniques, make stormwater practitioners aware of this potential issue. California Department of Transportation (June 26, 2002). An equally important and related parameter that is not as Johnson, M. L., and L. C. Hall. The Estrogenicity of Selected Her- frequently monitored as sediment concentration is the sedi- bicides and Adjuvants Endocrine Disruption Capabilities of Sur- ment particle-size distribution. Particle size plays an impor- flanTM and Oryzalin. Caltrans Report, Division of Environmen- tant role in the transport and aquatic biota impacts of mobi- tal Analysis (2002). lized sediment. Particle size distribution also seems to play Kayhanian, M., Murphy, K., Regenmorter, L., and R. Haller. Char- an important role in the transport of some metals, nutrients, acteristics of Stormwater Runoff from Highway Construction and trace organics. Monitoring for particle size and these Sites in California. In Transportation Research Record: Journal other parameters could increase significantly the costs of a of the Transportation Research Board, No. 1743, TRB, National construction project. It would be beneficial to have an initial Research Council, Washington, DC (2001) pp. 3340. Powell, S., Neal, R., and J. Leyva. Runoff and Leaching of Simazine screening method for assessing the quality of site soils on a and Diuron Used on Highway Rights-of-Way. Environmental grain-size basis to determine the level of monitoring as well Hazards Assessment Report EH 96-03, California Environmen- as sediment and erosion controls necessary to prevent impacts tal Protection Agency, Department of Pesticide Regulations, to receiving waters. Environmental Monitoring and Pest Management Branch (1996). It is apparent from the literature reviewed that additional Wood, T. M. Herbicide Use in the Management of Roadside Vege- work is needed in the area of roadside vegetation manage- tation, Western Oregon, 19992000: Effects on the Water Qual- ment. The potential for herbicides to migrate from roadsides ity of Nearby Streams. Investigation Report 01-4065, U.S. Geo- to receiving waters is strongly dependent on the type of logical Survey, Water-Resources Investigation, Washington, DC chemical applied (i.e., depends primarily on solubility and (2001) 27 pp. hydrophobicity). Numerous herbicides are in use by DOTs throughout the 3.4.9. Drain Inlet and Gross Pollutant Studies country, of which only a small number have been tested for their mobility and potential toxicity to aquatic biota. Most The control of gross pollutants in highway runoff was studies have been conducted under highly controlled condi- addressed in section 3.2.2., Gross Pollutant Removal. This tions in a laboratory or by using simulated rainfall. Further- section focuses on the characterization of gross pollutants in more, toxicity studies have been conducted at higher con- highway runoff. centrations than likely to occur at the rates applied. More Gross pollutants can be grouped loosely into three cate- herbicide runoff characterization studies during storm condi- gories: litter or trash, debris, and coarse sediments. Exam- tions are needed in conjunction with toxicity studies at the ples of litter include unwanted anthropogenic waste materi- concentrations found. Furthermore, an analysis of the adsorp- als such as paper, metal, glass, and plastic. Examples of tion of herbicides to various grain sizes would assist in deter- debris include organic materials such as grass, leaves, and mining the potential for migration. Once more information is wood. Coarse sediments consist mainly of inorganic solids available on potential impacts of herbicides, a detailed cost such as construction materials and soil particles (England benefit comparison of using herbicides as opposed to other and Rushton, 2003). Gross solids can cause odors, release vegetation control methods, such as manual clearing, should pollutants, and become an unsightly mess; yet gross solids be considered. are monitored infrequently as are other pollutants in many of the studies available (England and Rushton, 2003). Improp- 22.214.171.124. Primary References erly disposed gross solids can be carried by stormwater or wind to water bodies, causing environmental degradation Barrett, M. E., Zuber, R. D., Collins, E. R., Malina, J. F., Charbeneau, (Sedrak et al., 2001). Factors that determine the mobility and R. J., and G. H. Ward. A Review and Evaluation of Literature persistence of gross solids include buoyancy, the ability to be
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120 blown around by the wind, and degradability (Sedrak et al., drainage systems. Two of the BMPs that the researchers tested 2001). Research questions and areas of interest with respect increased litter pick-up, and the modified drain inlet substan- to gross solids management include tially reduced litter. Street sweeping, the bicycle grate, and the Litter Inlet Deflector were ineffective in controlling litter. · Sources of gross solids, The importance of the effects of water velocity and depth · Gross solids monitoring measuring techniques, in the transport of gross solids was investigated by Davies · Gross solids impacts to stormwater and receiving water et al. (1998). The authors presented the results of a labora- systems, and tory study on solids advection with applications in solids trans- · Gross solids modeling and estimation techniques. port modeling. Milne et al. (1996) collected and analyzed gross solids in an attempt to estimate the related impacts and Several studies are available that define and characterize interaction with sediment. They sampled wet and dry weather gross solids. Armitage and Rooseboom (2000) presented a flows and monitored gully discharge. discussion that defines urban litter, identifies sources of lit- ter, and suggests litter management strategies. Factors iden- tified as contributing to litter problems included antisocial 126.96.36.199. Identification of Research Gaps behavior, excessive packaging, inadequate street sweeping and Needs services and disposal facilities, and lack of effective law Because of the variety of materials that make up gross pol- enforcement. The authors noted that the rate of litter produc- lutants in highway runoff, characterization and assessment is tion is related to type of development, density of development difficult. Areas that appear to be well covered in the litera- or land use, income level of the community, types of indus- ture include the determination of sources of gross solids and try, rainfall patterns, types of vegetation in the catchment, and the composition, characteristics, and transport of gross solids. the level of a community's environmental awareness. The Most researchers quantify gross pollutants by either weight authors conclude by providing a discussion of litter load esti- or volume, and some segregate according to material type, mation with equations for evaluating litter quantities for such as plastic or metals. For the purposes of data transfer, design purposes. there appears to be a need for the development of standard The results of a comprehensive study showed that plastics methods for quantifying gross pollutants. As mentioned in made up more than 40% (by weight) of the floatable litter section 3.2.2, a potential research need may be to identify a found on the streets of New York City. Details of this study are uniform definition of gross solids (and its components) for provided by England et al. (2003) in addition to simple meth- purposes of standardizing the reporting of data. There also ods for measuring and characterizing gross solids removed by appears to be a need for more studies on receiving water various BMPs for both wet and dry weather. A study pre- impacts of gross solids, with a particular need for modeling sented by Sedrak et al. (2001) identified high trash generat- and estimation techniques for gross solids especially in rela- ing areas in Los Angeles and proposed both structural and tion to TMDLs. nonstructural controls to manage trash. This study also found Another potential research gap may be the leaching or that plastics are the single largest component of trash. Trash sorption capacity, or both, of pollutants captured in catch enters receiving water bodies mainly by direct disposal by basins. For instance, cigarette butts, which can contribute as hikers or beachgoers, stormwater, and wind. The authors much as 10% by dry weight of all street litter (City of Los concluded that commercial, industrial, and residential land Angeles, 2001), contain several toxic and carcinogenic com- use areas produce the most trash. They suggested nonstruc- pounds that may leach to receiving waters during storm- tural trash control measures including street sweeping, catch water runoff events. On the other hand, bulk paper trash may basin cleaning, antilittering statutes, abandoned trash hot- aid in the sorption of oil and grease in stormwater runoff. lines, trash cans, educational programs, and community clean- up programs. Structural trash or litter controls suggested include Continuous Deflective SeparationTM units, Netting 188.8.131.52. Primary References Trash TrapTM, catch basin inserts, and catch basin opening covers. Armitage, N., and A. Rooseboom. The Removal of Urban Litter In a Caltrans study, Lippner et al. (2001) investigated the from Stormwater Conduits and Streams: Paper 1--The Quanti- characteristics of litter in highway stormwater and evaluated ties Involved and Catchment Litter Management Options. Water SA, Vol. 26, No. 2 (April 2000) pp. 181187. the effectiveness of BMPs by conducting a 2-year pilot study City of Los Angeles. High Trash-Generation Areas and Control in the Los Angeles area. The researchers found that plastic, Measures. Report, Department of Public Works, Bureau of San- paper, and Styrofoam constituted about 42% by weight and itation (2001). 57% by volume of total freeway litter. Securing a mesh bag on Davies J. W., Sekuloski, V., and D. Butler. Inclusion of Gross an outfall with VelcroTM worked well as a monitoring tech- Solids Advection and Deposition in Urban Drainage Models. nique, however the suggested monitoring technique is not rec- Proc., 4th International Conference on Developments in Urban ommended for outfalls that directly connect to other subgrade Drainage Modeling (September 1998) pp. 365372.
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121 England G., and B. Rushton. Monitoring Guidelines for Measuring snow event, except for the finest solid class, which showed a Stormwater Gross Pollutants. Proc., STORMCON Conference, slight increase with time. In contrast to zinc, lead concentra- Session M-103, San Antonio, TX (July 2003). tions on rainfall runoff solids were generally lower than on Lippner, G., Johnston, J., Combs, S., Walter, K., and D. Marx. snow solids. Results of California Department of Transportation Litter Man- In their highway runoff monitoring study in Lake Tahoe, agement Pilot Study. California Water Environment Association Caltrans (2002) characterized particles removed from the sand (CWEA) 72nd Annual Conference, Sacramento (April 1619, 2000). traps and filter boxes using the sieve and hydrometer method. Milne, D. A., Jefferies C., and R. M. Ashley. Pollutional Aspects of Particle sizes ranged from less than 2 µm to more than 9500 Gross Solids and Their Interaction with Sewer Sediments. Water µm, with the majority of particles falling in the range from 100 Science and Technology, Vol. 33, No. 9 (1996) pp. 3137. to 2000 µm. These mid-sized suspended particles are rela- Sedrak, M. F., Tam, W. K., Kaporis, K., and J. Pang. High Trash- tively large and over a relatively short period settle easily out Generation Areas and Control Measures. (August 2001) 36 pp. of suspension because of gravity. Yet, the remaining colloidal (0.001 µm1 µm) and smaller suspended particles tend to remain suspended in waters because of their low gravitational 3.4.10. Cold-Weather Studies settling (less than 0.01 cm/sec) which could cause an increase in turbidity. It should be noted that in their study about the Cold-weather highway runoff quality studies primarily effectiveness of double barrel sand traps, removal of more than characterize snowmelt runoff and evaluate winter mainte- 90% of the total mass of TSS did not remove total phosphorus nance activities such as highway sanding and deicing agent to the same degree (i.e., less than 20%). Particles associated application. This field also encompasses studies that evalu- with the snow ranged from 5000 µm to less than 25 µm and ate the effects of frozen soil on runoff and infiltration rates, had a d50 of 1222 µm. Specific gravity ranged from 2.5 to 3.2 as well as snowbank pollutant accumulation studies. Finally, and tended to be lower for particles less than 100 µm. Metal a few studies have looked at the functioning of BMPs during analyses of the snow residuals indicated that 50% of the heavy cold weather. Compared to stormwater runoff, snow exposed metal mass of lead, copper, cadmium, and zinc was bound to to traffic and winter maintenance practices has a much greater particles greater than 250 µm. capacity to accumulate and retain heavy metals, fine dusts, The treatment of snowmelt runoff is confounded by sev- and other anthropogenic constituents. Traffic activities and eral factors including frozen conduits, ponds, soils and wet- winter storm management practices can have a significant lands, biological dormancy, and the addition of chemicals impact on pollutant accretion in urban snow. Urban snow- and grit to roadways (Oberts, 2000). Adaptation of com- packs accumulate large quantities of solids and contami- monly used BMPs can be undertaken to accomplish some nants, which originate from such sources as airborne fallout, level of treatment, such as modifying outlet structures on vehicular deposition, and applied and ground up grit and salt. detention ponds and using new subsurface "vault" treatment Both contaminants and solids may be released quickly dur- systems. Other measures include selective use of deicing ing the periods of snowmelt, and consequently melting con- chemicals (see section 3.5.7 for discussion on deicing impacts taminated snow in urban areas in cold climates has the poten- to receiving waters) and constructing road snow storage tial to impact substantially the water quality of receiving areas. However, there is still significant research needed in waterbodies (Oberts, 2000; Smith et al., 2000). Cristina et al. this area. (2001) and Sansalone and Glenn (2001), in their detailed The results of some of the more recent cold weather stud- studies involving physical and chemical characterization of ies, such as those discussed above, indicate the quality of snowmelt runoff, indicated that extended residence times of snowmelt runoff from highways may be highly degraded and snow as a roadway snowbank exposed to traffic activities and may be seriously impacting receiving streams. This realiza- winter maintenance practices lead to significant pollutant tion, combined with the implementation of the NPDES Phase accretion and partitioning in the snow matrix. Several other II stormwater regulations, is causing an increasing interest in studies discuss the accumulation of pollutants in the snow nonpoint source control of cold climate runoff. In fact, a first- and eventual shock loading of pollutants during snowmelt or of-its-kind North American 3-day stormwater conference rain on snow events (Thorolfsson, 1999; Hatch et al., 1999). entitled Stormwater Management in Cold Climates: Planning, In another study, Sansalone and Buchberger (1997) pre- Design, and Implementation was held in Portland, Maine, in sented the effect of snowbank residence time on PSDs and November 2003 to focus specifically on the challenge of man- particulate-bound metal element concentrations for two snow aging stormwater in cold climates (http://www.cascobay. events. Results indicated that for each snow event, increas- usm.maine.edu/coldsw.html). ing residence time of the snowbank did not result in a clear increase in zinc, cadmium, or copper concentrations. Zinc concentrations on solids from rainfall events were signifi- 184.108.40.206. Identification of Research Needs cantly higher than for snow events. Snowbank lead concen- trations decreased over time for the finer fractions of solids Based on the literature review, there is clearly a need for for the first snow event with a similar trend for the second more monitoring and characterization of snowmelt runoff