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From page 12... ... 12 This chapter describes the basis for the pollutant categories included in this report and provides guidance on how to determine the significance of stormwater POCs for roadways in relation to TMDLs and impaired water bodies. In the preliminary phases of TMDL development, an understanding of the watershed's POCs and their associated land use contributions can assist state DOTs in determining the appropriate engagement and implementation strategy. Read the entire page →
From page 13... ... Significance of Stormwater Pollutants 13 the types of pollutants that would be expected to contain roadway WLAs, since a similar approach is used for both current and future TMDL development. Read the entire page →
From page 14... ... 14 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff Cause Group Water Bodies, Urban Runoff Impairment TMDLs, Transportation Agencies Listed Percentage of 27,036 TMDLsa Primary Classification (proportion of group total) b Percentage of 5,340 TMDLsa Primary Classification (proportion of group total) Read the entire page →
From page 15... ... Significance of Stormwater Pollutants 15 body measurements that were difficult to translate to land use WLAs. This limitation can result in the selection of alternative cause classifications that are more specific or delay the TMDL development until quantifiable impairment causes are identified. Read the entire page →
From page 16... ... 16 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff TMDL development and to research how other jurisdictions are structuring TMDLs for the same constituents or constituent categories. The following data sources may be useful to state DOT practitioners to identify impaired water bodies and developed TMDLs, as well as for other types of watershed information: 1. Read the entire page →
From page 17... ... Significance of Stormwater Pollutants 17 • National Stormwater Quality Database (NSQD) : The NSQD is a compilation of monitoring data collected by NPDES permit holders. Read the entire page →
From page 18... ... 18 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff • Residential: Housing areas of low-to-high density and mixed-use areas that are predominantly residential. • Open Space: Undeveloped or preserved areas, including grasslands, forests, and parks. Read the entire page →
From page 19... ... Significance of Stormwater Pollutants 19 Land Use Category Median Concentrations of All Data from All Sites Combined (25th to 75th percentiles of all data from all sites combined) Read the entire page →
From page 20... ... Land Use Category Median Concentrations of All Data from All Sites Combined (25th to 75th percentiles of all data from all sites combined) Aluminum µg/L Arsenic µg/L Cadmium µg/L Copper µg/L Iron µg/L Lead µg/L Manganese µg/L Mercury µg/L Zinc µg/L Highway (AADT 0–25K) Read the entire page →
From page 21... ... Land Use Category Quantity of Sites/Samples (percentage of samples non-detect) Read the entire page →
From page 22... ... Land Use Category Median Concentrations of All Data from All Sites Combined (25th to 75th percentiles of all data from all sites combined) Read the entire page →
From page 23... ... Significance of Stormwater Pollutants 23 The size of the data set should be considered when evaluating its applicability as a calculation input, including the following: • Sediment and Nutrients (Tables 3 and 4) : The nutrient and sediment data sets are relatively robust for all constituents and land uses. Read the entire page →
From page 24... ... 24 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff Presumably, the predominant source of sediment from roadways and other land uses is the adjacent in situ soil or fill material. An understanding of the background pollutant soil concentrations and the particulate-bound washoff characteristics is used to assess the proportion of pollutant runoff concentrations that are potentially attributed to soil concentrations. Read the entire page →
From page 25... ... Significance of Stormwater Pollutants 25 phosphorus and metal analytes (https://mrdata.usgs.gov/soilgeochemistry/#/summary) Read the entire page →
From page 26... ... 26 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff than roadway runoff concentrations. This indicates that the source of iron in highway runoff may often be primarily background soils. Read the entire page →
From page 27... ... Significance of Stormwater Pollutants 27 monitoring data or land use summary statistics, as described in Tables 14 to 20 of this chapter. Storm event runoff loads are computed from the EMCs and hydrologic parameters to estimate instream concentrations upstream and downstream of a site. Read the entire page →
From page 28... ... 28 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff 4. Repeated Step 3 for each of the atmospheric deposition pollutants to determine the proportion of highway runoff contribution to each pollutant attributed to deposition. Read the entire page →
From page 29... ... Significance of Stormwater Pollutants 29 State DOTs across the nation whose sampling data indicate ammonium ion concentrations close to the national 25th percentile concentration should evaluate atmospheric deposition as a possible significant contributor. Similarly, Figure 10 indicates that, for state DOTs located in certain parts of the country, sample concentrations close to the 75th percentile national average concentration could still attribute a significant portion of their loads to atmospheric deposition. Read the entire page →
From page 30... ... 30 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff country (Figure 12) Read the entire page →
From page 31... ... Significance of Stormwater Pollutants 31 from 0.1 µg/L to 1 µg/L) Read the entire page →
From page 32... ... 32 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff Proportion of Chloride Potentially Attributed to Atmospheric Deposition >0.30 0.17–0.30 0.10–0.17 0.05–0.10 0.0–0.05 Figure 16. Estimated proportion of 75th percentile highway chloride ion concentration attributed to atmospheric deposition from 2016 NTN data. Read the entire page →
From page 33... ... Significance of Stormwater Pollutants 33 lower than the concentrations shown in the figure can conclude that atmospheric deposition is not a significant contributor. However, those with measured concentrations close to the values shown can justify further investigation to quantify the contribution of atmospheric deposition. Read the entire page →
From page 34... ... 34 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff to combined wet and dry deposition. In urban settings, much of this deposition may be from local sources, such as emissions and airborne dust from vehicles and industry. Read the entire page →
From page 35... ... Significance of Stormwater Pollutants 35 was added to account for differences in roadway definition. The 100 percent impervious category is representative of roads with curbs, gutters, and a piping system, whereas the 60 percent impervious category is representative of an entire highway corridor (including medians, shoulders, and drainage swales) Read the entire page →
From page 36... ... 36 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff The results of the example SELDM analysis that quantified the unit area pollutant loads for the Pacific Northwest are shown in Figure 19. The exceedance probability represents the likelihood in any given year that the load from that land use will be greater than the specified value. Read the entire page →
From page 37... ... Significance of Stormwater Pollutants 37 Land Use Runoff Concentration Statistics The land use runoff concentration statistics presented in Tables 14 to 20 are organized by land use type and provide the necessary input statistics for defining a water quality constituent in SELDM. SELDM can be used to generate unit loading rates for the POCs identified in Table 2 for various land uses. Read the entire page →
From page 38... ... 38 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff Constituent Unit Sites Samples Non-Detect (%) Ln Mean Ln SD Ln Skew Geomean AADT 0–25K TSS mg/L 32 665 1 3.802 1.530 0.016 44.8 TKN mg/L 28 492 16 -0.262 1.177 -0.117 0.770 NO2,3 as N mg/L 13 207 2 -0.816 0.828 0.397 0.442 TP mg/L 28 433 16 -2.251 1.451 0.226 0.105 DP mg/L 4 46 7 -2.552 0.532 0.034 0.078 Arsenic µg/L 19 339 56 -0.386 1.525 0.048 0.680 Cadmium µg/L 27 446 51 -2.048 2.088 0.235 0.129 Copper µg/L 35 651 10 2.239 1.156 0.051 9.38 Iron µg/L 13 241 3 6.931 1.994 -0.009 1024 Lead µg/L 33 621 21 2.088 2.208 -0.032 8.07 Manganese µg/L 3 32 0 3.423 1.334 -0.199 30.7 Zinc µg/L 35 639 2 4.104 1.104 0.029 60.6 Fecal Coliform MPN/100 mL 2 4 0 10.384 2.478 0.365 32323 BOD mg/L 6 66 8 1.649 0.612 0.502 5.20 Cl- mg/L 12 423 4 3.115 2.256 0.249 22.5 TDS mg/L 1 4 0 3.761 0.253 -1.021 43.0 AADT 25–50K TSS mg/L 15 266 <1 4.069 1.343 0.208 58.5 TKN mg/L 13 164 1 0.631 0.804 -0.022 1.88 NO2,3 as N mg/L 12 123 <1 -0.250 0.793 -0.457 0.779 TP mg/L 18 266 7 -1.935 1.226 0.543 0.144 DP mg/L 4 41 22 -2.437 0.987 -0.245 0.087 Arsenic µg/L 10 151 17 0.240 1.043 0.387 1.27 Cadmium µg/L 17 226 13 -1.026 1.208 0.188 0.358 Copper µg/L 21 301 10 2.931 0.922 -0.148 18.74 Iron µg/L 12 193 0 7.491 1.236 0.289 1792 Lead µg/L 21 301 4 2.647 1.609 0.166 14.12 Manganese µg/L 6 70 0 3.676 0.918 0.358 39.5 Zinc µg/L 21 313 <1 4.569 1.290 0.208 96.4 Fecal Coliform MPN/100 mL 1 9 0 6.526 1.026 -1.316 683 BOD mg/L 5 39 3 1.413 0.785 -0.275 4.11 Cl- mg/L 10 605 0 3.978 2.181 0.895 53.4 AADT 50–100K TSS mg/L 27 598 <1 4.449 1.226 -0.600 85.5 TKN mg/L 21 335 <1 0.506 0.738 -0.116 1.66 NO2,3 as N mg/L 11 120 0 -0.195 0.986 -0.288 0.822 TP mg/L 20 329 6 -1.768 0.960 -0.440 0.171 DP mg/L 3 28 32 -2.618 1.042 -0.136 0.073 Arsenic µg/L 9 152 32 0.074 1.022 0.985 1.08 Cadmium µg/L 23 334 13 0.224 2.260 0.308 1.25 Copper µg/L 27 561 2 3.453 1.024 -0.065 31.6 Iron µg/L 9 203 0 8.412 1.010 -0.334 4502 Lead µg/L 27 550 3 4.079 2.397 -0.129 59.1 Manganese µg/L 2 28 0 4.063 1.041 0.462 58.1 Zinc µg/L 27 501 <1 5.104 0.922 -0.197 165 Fecal Coliform MPN/100 mL 3 15 0 7.710 1.541 0.070 2230 BOD mg/L 8 112 <1 2.580 0.839 -0.010 13.2 Cl- mg/L 10 568 <1 3.613 2.104 0.728 37.1 Table 15. Read the entire page →
From page 39... ... Significance of Stormwater Pollutants 39 Constituent Unit Sites Samples Non-Detect (%) Ln Mean Ln SD Ln Skew Geomean AADT 100k+ TSS mg/L 45 873 <1 4.416 1.285 -1.379 82.8 TKN mg/L 38 567 2 0.544 0.873 -0.128 1.72 NO2,3 as N mg/L 22 290 <1 -0.173 0.789 0.101 0.841 TP mg/L 43 559 2 -1.510 0.940 -0.136 0.221 DP mg/L 8 54 2 -1.923 1.333 0.461 0.146 Arsenic µg/L 23 325 23 0.542 0.961 0.404 1.72 Cadmium µg/L 46 586 6 0.000 1.261 0.740 1.00 Copper µg/L 48 779 6 3.620 1.100 -0.252 37.3 Iron µg/L 16 150 0 8.292 1.304 -0.405 3993 Lead µg/L 49 717 1 3.870 1.855 0.140 47.9 Manganese µg/L 9 55 0 4.834 1.068 -0.211 125.7 Mercury µg/L 4 15 100 -2.190 0.486 -1.055 0.112 Zinc µg/L 49 796 0 5.277 1.179 -0.959 196 Fecal Coliform MPN/100 mL 6 56 0 7.961 2.191 0.423 2868 BOD mg/L 12 118 2 1.866 1.025 1.368 6.46 Cl- mg/L 13 583 <1 4.381 2.188 0.635 79.9 TDS mg/L 1 4 0 4.931 1.312 -0.170 139 Ln = natural log; SD = standard deviation; Geomean = geometric mean = exp(Ln Mean) Read the entire page →
From page 40... ... 40 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff Constituent Unit Sites Samples Non-Detect (%) Ln Mean Ln SD Ln Skew Geomean TSS mg/L 97 1,225 <1 3.987 1.481 -0.373 53.9 TN mg/L 13 144 3 0.550 0.883 -0.409 1.73 TKN mg/L 88 973 6 0.343 0.881 0.258 1.41 NO2,3 as N mg/L 76 856 5 -0.643 1.022 -0.420 0.526 TP mg/L 104 1,203 4 -1.490 1.067 0.048 0.225 DP mg/L 16 301 24 -2.418 1.553 -0.021 0.089 Aluminum µg/L 3 24 4 7.275 1.782 -0.352 1444 Arsenic µg/L 27 179 73 -1.017 1.833 0.060 0.362 Cadmium µg/L 58 692 49 -1.006 1.952 0.199 0.366 Copper µg/L 91 1,109 10 2.377 1.399 -0.365 10.8 Iron µg/L 2 18 0 8.318 1.303 0.093 4097 Lead µg/L 80 875 21 2.170 1.799 -0.088 8.8 Mercury µg/L 23 186 95 -2.109 1.175 1.449 0.121 Zinc µg/L 97 1,166 2 4.219 1.460 -0.693 68.0 E Read the entire page →
From page 41... ... Significance of Stormwater Pollutants 41 Constituent Unit Sites Samples Non-Detect (%) Ln Mean Ln SD Ln Skew Geomean TSS mg/L 250 4,011 <1 4.018 1.440 -0.289 55.6 TN mg/L 44 766 3 0.461 0.810 -0.325 1.59 TKN mg/L 224 3,084 2 0.302 0.878 -0.240 1.35 NO2,3 as N mg/L 213 3,112 2 -0.670 1.050 -0.731 0.512 TP mg/L 271 4,146 2 -1.466 1.044 -0.234 0.231 DP mg/L 39 1,192 5 -2.631 1.308 -0.440 0.072 Arsenic µg/L 64 673 56 0.034 1.210 0.090 1.03 Cadmium µg/L 125 1,658 55 -1.356 1.801 0.066 0.258 Copper µg/L 216 2,792 10 2.448 1.349 -0.190 11.6 Iron µg/L 14 347 3 6.918 1.583 -0.596 1010 Lead µg/L 184 2,373 19 2.128 1.768 -0.128 8.40 Manganese µg/L 5 225 7 4.103 0.944 -0.063 60.5 Mercury µg/L 44 360 80 -5.844 5.334 0.441 0.003 Zinc µg/L 230 3,213 3 4.240 1.388 -0.457 69.4 BOD mg/L 161 1,887 5 2.121 0.928 0.055 8.34 E Read the entire page →
From page 42... ... 42 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff These data were further analyzed to estimate land use summary statistics for each constituent for user input into the model (Tables 14–20) Read the entire page →

From page 12...

... 12 This chapter describes the basis for the pollutant categories included in this report and provides guidance on how to determine the significance of stormwater POCs for roadways in relation to TMDLs and impaired water bodies. In the preliminary phases of TMDL development, an understanding of the watershed's POCs and their associated land use contributions can assist state DOTs in determining the appropriate engagement and implementation strategy.