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3 Guidance on Modeling Offsite Deposition of 

4 Pesticides Via Spray Drift for Ecological and 

5 Drinking Water Assessments

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21 Katrina White, Ph.D., Faruque Khan, Ph.D.,

22 Charles Peck, Mark Corbin, M.S.

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24 Environmental Fate and Effects Division

25 Office of Pesticide Programs

26 U.S. Environmental Protection Agency

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28
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29 ACKNOWLEDGEMENTS

30

31 The authors would like to acknowledge the input from two key former EFED workgroups, the 

32 Endangered Species Registration Review Workgroup and Litigation Steering Committee. 

33 Additionally, this document was reviewed by representatives of other technical teams in EFED,

34 including Kristina Garber, Nicholas Mastrota, Gabe Rothman, Michael Davy, and Greg Orrick. 

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39 Table of Contents

40

41 1. Purpose of Guidance............................................................................................................. 4

42 2. Offsite Deposition of Pesticides and Spray Drift Distance ................................................ 4

43 2.1. Initial Inputs/Setup for AgDRIFT for Terrestrial and Aquatic Assessments.................. 5

44 2.2. Modeling Exposure to Terrestrial Organisms Off the Field........................................... 7

45 2.2.a Estimating Exposure off the Field .............................................................................. 7

46 2.2.b Estimating the Terrestrial Spray Drift Distance.......................................................... 7

47 2.3. Modeling Exposure to Aquatic Organisms Off the Field................................................ 9

48 2.3.a Estimating the Aquatic Spray Drift Fraction for Use in PRZM/EXAMS at a 

49 Specified Distance from the Edge of the Field ..................................................................... 10

50 2.3.b Estimating the Aquatic Spray Drift Distance............................................................ 12

51 2.4. Reporting on Modeling Procedures, Results, and Uncertainties ................................. 16

52

53 List of Appendices

54

55 Appendix A. Comparison of Results from Tier I, Tier II, and Tier III AgDRIFT Analysis Using 

56 the ASAE Very Fine to Fine DSD and Fine to Medium DSD............................... 18

57 Appendix B. How to Determine the Aquatic and Terrestrial Spray Drift Fraction for an 

58 Application Rate in AgDRIFT for Ecological Assessments.................................. 21

59 Appendix C. Calculation of the Spray Drift Fraction for Drinking Water Assessments Using the 

60 Index Reservoir. ..................................................................................................... 27

61 Appendix D. Example and Validation of Terrestrial Spray Drift Distance Approach ................ 29

62

63
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64 1. Purpose of Guidance

65

66 During the application of pesticides, an appreciable amount of applied chemical can drift beyond 

67 the intended target site to non-target receptors and their habitats or surface water sources. The 

68 purpose of this document is to provide guidance on modeling offsite deposition of pesticides 

69 through spray drift for ecological and drinking water assessments. Additionally, this guidance

70 provides standard default assumptions for quantifying pesticide deposition from spray drift to

71 terrestrial and aquatic environments and information on the characterization of spray drift buffers 

72 used to mitigate identified risks for non-listed species. The Agency is in the process of 

73 evaluating its approach for assessing offsite deposition impacts to listed species, given the 

74 recommendations outlined in the recent National Academy of Sciences publication “Assessing 

75 Risks to Endangered and Threatened Species from Pesticides” (NAS, 2013). Once the Agency, 

76 the Fish and Wildlife Service, and National Marine Fisheries Service agree on a common 

77 approach for the ecological risk assessment process for listed species, this document will be 

78 revised accordingly. This document does not provide guidance regarding off-site transport 

79 through other mechanisms such as vapor drift, wet and dry deposition, long-range transport, as 

80 well as surface water runoff and downstream movement of a compound.

81 2. Offsite Deposition of Pesticides and Spray Drift Distance

82

83 Exposure to spray drift is assessed for agricultural and residential spray applications of liquid 

84 formulations, except for applications with hand held or back pack sprayers. EFED does not 

85 currently have a method to quantify spray drift from other application methods and materials 

86 such as applications of dry materials, drip chemigation, and for applications with hand held or 

back pack sprayers; therefore, spray drift is assumed to be negligible. AgDRIFT1 87 can be used to 

88 model spray drift in the following ways:

89

90 • Estimate the spray drift fraction for inputs into PRZM/EXAMS for estimating aquatic 

91 exposure in drinking water and ecological risk assessments

92 • Estimate exposure of plants to spray drift in ecological risk assessments

93 • Estimate the fraction of applied pesticide, used in assessing exposure for terrestrial organisms 

94 located off the application site, including for applications directly to water 

95 • Determine the maximum distance from the edge of the area where the pesticide is directly 

96 applied (also known as the initial area of concern) to the point where levels of concern 

97 (LOCs) are no longer exceeded for both terrestrial and aquatic organisms. 

98

99 In addition to AgDRIFT, the following models may be needed to estimate spray drift distances 

100 for terrestrial and aquatic organisms:

101

• Terrestrial Residue Exposure model (T-REX)2 102

 1 Spray Drift Task Force Spray Software. AgDRIFT (Version 2.1.1). Available at G:\Models_Repository\AgDRIFT 2 USEPA 2008. Terrestrial Residue Exposure Model. Available at 

http://www.epa.gov/oppefed1/models/terrestrial/trex/t_rex_user_guide.htm
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• Terrestrial Herpetofaunal Exposure Residue Program Simulation (T-HERPS)3 103 to estimate the 

104 spray drift distance for terrestrial organisms 

• Pesticide Root Zone Model (PRZM)4 105 and the Exposure Analysis Modeling System 

(EXAMS)5 106

107

108 Spray drift distances are distances from the edge of the field where LOCs may be exceeded and 

109 they are important in determining possible options for mitigating risk. For screening level 

110 assessments, spray drift analysis should be limited to the Tier I module in AgDRIFT unless the 

111 label specifies certain application parameters to limit spray drift potential. For example, use of a 

112 helicopter or applications at wind speeds of 15 mph would require use of Tier II or III modeling 

113 in AgDRIFT. Tier II and III modules are only available for aerial applications. Tier II and III

114 modules allow the user to modify many variables pertinent to spray drift to make the scenario 

more representative.6 115 In general, Tier II and III modules are used for refining geographic extent 

116 of risk and mitigating risk. The assessor may consider using both the Tier II and III modules in 

117 AgDRIFT on a case-by-case basis. The maximum spray drift distance using Tier I and II 

118 analyses is 997 feet and the maximum spray drift distance using Tier III analysis is 2608 feet. 

119 Aquatic and terrestrial assessment results for Tier II and III analyses are similar to the results 

from Tier I analysis with the ASAE (American Society of Agricultural Engineers)

7 120 Very Fine to 

121 Fine drop size distribution (DSD) across a range of target deposition values (Appendix A). Tier 

122 II and III analyses will require justification when using input parameters that deviate from the 

123 default parameters. The AgDRIFT module for modeling multiple applications should not be 

used.

8 124 Consult the Fate Tech Team and Water Quality Tech Team for guidance on modeling 

ultra low volume (ULV) applications9 125 . 

126 2.1. Initial Inputs/Setup for AgDRIFT for Terrestrial and Aquatic 

127 Assessments

128

129 • Open AgDRIFT and choose the appropriate Tier for your assessment. 

130 • Unless parameters are specified on the label, select the appropriate default input parameters 

 3 USEPA 2008. Terrestrial Herpetofaunal Exposure Residue Program Simulation. Available at 

http://www.epa.gov/oppefed1/models/terrestrial/therps/t_herps_user_guide.htm

4 USEPA 2006. Pesticide Root Zone Model. Available at http://www.epa.gov/oppefed1/models/water/#przm 5 USEPA 2005. Exposure Analysis Modeling System. Available at 

http://www.epa.gov/ceampubl/swater/exams/index.html

6 Tier II allows the user to modify drop size distribution (DSD), nonvolatile application rate, active application rate, 

spray application rate, carrier type (water or oil), wind speed, temperature, relative humidity, aircraft type, boom 

length, boom height, number of swaths, swath width, and swath displacement. The Tier III module allows the user 

to access all model inputs including the Spray Drift Task Force (SDTF) spray materials evaporation library, wind 

direction, the SDTF aircraft library, nozzle positioning, surface roughness, and access to the Spray Block Statistics 

calculator for inferring swath width, Coefficient of Variation (COV), and mean deposition within the spray block for 

input conditions specified to the model.

7 ASAE has been replaced by the American Society of Agricultural and Biological Engineers (ASABE); however, 

AgDRIFT is still using the ASAE abbreviation. In the future, labels may list ASABE standards rather than ASAE. 8 Note that PRZM/EXAMs will assume spray drift with each application, and multiple applications are also 

considered in T-REX to arrive at the target fraction of applied. So while EFED does not use this module, exposure 

to multiple spray drift events is considered in the risk assessment.

9 An ultra low volume application is a method of dispensing liquid pesticides at the rate of one half gallon or less per 

acre.
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131 as shown below. 

132

133 Agricultural, Golf Courses, and Residential Scenarios

134

a. Tier I Ground Applications: high boom height10 135 , ASAE Very Fine to Fine Drop Size 

Distribution (DSD), a 90th 136 percentile data percentile, do not access extended 

137 settings 

b. Tier I Aerial Application: use ASAE Fine to Medium DSD11 138

c. Tier I Orchard/Airblast: Sparse (Young/Dormant)12 139 : do not access extended settings

140

141 • Click on Toolbox and choose aquatic assessment for the aquatic environment or terrestrial 

142 assessment for the terrestrial environment.

143

144 Current default assumptions for aerial applications in AgDRIFT include the following:

145 • a wind speed of 10 mph, 

146 • 60-foot swath width, 

147 • release height of 10 feet,

148 • boom length: 76.3%, and

149 • swath displacement definition: fraction of swath width 0.3702.

150

151 If the label specifies that aerial application parameters beyond Tier I may occur (e.g., higher 

152 wind speeds or release heights), use Tier II or Tier III, whichever is applicable. If these best 

153 management practices are not followed and are not on the label, spray drift may be greater than 

154 that predicted using default input parameters and Tier I analysis. This information should be 

155 included in the risk assessment. If the evidence indicates that applications will likely not be 

156 consistent with the default assumptions (for example, the ASAE Fine to Medium DSD), the 

157 expected application parameters should be modeled in AgDRIFT. 

158

159 Generally, any changes made to these initial input parameters should be based on enforceable 

160 statements on labels. When a buffer distance is specified on a label, the number is placed in the 

161 “Distance to Water Body from Edge of Field” in the AgDRIFT aquatic or terrestrial assessment 

162 screen to estimate the spray drift fraction for inputs into PRZM/EXAMS or inputs into T-REX if 

163 assessing risk off the field (e.g., for an aquatic application). If different labels have different use 

164 restrictions, ensure that the input parameter(s) modeled is the most conservative (e.g., results in 

165 the highest percentage of spray drift or longest spray drift distance) or show the range that is 

166 representative of all labeled directions. 

 10 In AgDRIFT, a low boom is 0.508 m or 20 inches in height and a high boom is 1.27 m or 50 inches in height. The 

assumed swath width is 45 ft.

11 The Very Fine to Fine DSD results in higher spray drift deposition than the ASAE Fine to Medium DSD 

assumption. If evidence is available indicating that the Very Fine to Fine DSD is likely to be used and it is allowed 

on the label, this DSD may be modeled instead of the ASAE Fine to Medium DSD. 

12 The orchard/airblast provides an estimate of the 50th percentile of drift. The empirical data supporting the 

development of airblast exposure was very limited, and a 90th percentile estimate is not available at this time.

Therefore, the orchard airblast exposure estimate is not an upper bound exposure estimate. Use of other 

orchard/airblast modules should be used carefully since the current estimate of exposure may not be conservative.

EFED plans on developing a methodology to provide a conservative exposure estimate for airblast uses in the future. 
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167 2.2. Modeling Exposure to Terrestrial Organisms Off the Field

168 2.2.a Estimating Exposure off the Field

169

170 T-REX estimates exposures to terrestrial animals from residues on potential food items found at

171 the site of application (i.e., on the field). For determining potential risk to terrestrial animals 

172 from dietary exposure off the site of application (e.g., including for applications made directly to 

173 water), T-REX can be used in conjunction with spray drift models (e.g., AgDRIFT). For 

174 terrestrial animals, under Terrestrial Assessment in AgDRIFT, select Point Deposition and input 

175 the buffer distance specified on the label under “Distance To Point or Area From Edge of Field.”

176 The “Fraction of Applied” for ground and aerial applications will give you the fraction of the 

177 application rate that organisms will be exposed to at the specified distance. Multiply the 

178 application rate by the Fraction of Applied for aerial and ground applications and use the product 

179 of the two as the input for the application rate in T-REX. For applications directly to water, T180 REX will be used to assess risk to terrestrial animals based on the conservative assumption that 

181 exposure at the edge of the field will be identical to exposure on the water body. For bare 

182 ground applications, use T-REX to estimate exposure on the field and explain that the EECs for 

183 seeds and insects reflect exposure on the field and exposure to residues on plants, which will 

184 mainly occur at the edge of the field. 

185

TerrPlant13 186 estimates exposure to plants adjacent to the site of application. The next section 

187 discusses how to estimate a distance from the edge of the field where terrestrial plants may be 

188 exposed to spray drift at levels that could result in a Level of Concern (LOC) exceedance (e.g., a 

189 spray drift distance).

190 2.2.b Estimating the Terrestrial Spray Drift Distance

191

192 Below are instructions for calculating a spray drift distance or the distance from the edge of the 

193 field where LOCs may be exceeded for terrestrial organisms. All spray drift distances should be 

194 rounded to a whole number.

195

Terrestrial Animals: Calculate the target14 “Fraction of Applied”15 196 for terrestrial animals based 

197 on risk quotients that are generated using T-REX or T-HERPS, acute and chronic terrestrial 

198 animal endpoints, and the appropriate LOCs. Risk quotients should be calculated using the 

maximum application rate and the maximum number of applications.16 199 For sublethal effects 

200 endpoints, the LOC is not established for acute sublethal effects and is assumed to be one in the 

 13 USEPA 2009. TerrPlant. Available at http://www.epa.gov/oppefed1/models/terrestrial/ 14 The target refers to that “fraction of applied” that will result in RQs being below LOCs.

15

Risk Quotient

Level of Concern

Aerial and Ground Applications Target Fraction of Applied =

0.5

Risk Quotient

Level of Concern

Airblast Applications Target Fraction of Applied = ×

16 While conceptually this calculation results in combining an RQ based on multiple applications in T-REX with a 

single exposure event for spray drift, the resulting spray drift distance will mitigate risk for both a single application 

and multiple applications. See Appendix D for validation of this approach.
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calculation of the target Fraction of Applied as specified in Footnote 15.

17 201 Under Terrestrial 

202 Assessment, select Point Deposition and input the target Fraction of Applied. Click on “Calc.” 

203 Figure 1 shows an example calculation. Inputs are “Point Deposition” and the “Fraction of 

204 Applied.” The output is the “Distance to Point or Area Average from Edge of Field,” and it 

205 represents the terrestrial spray drift distance. In Figure 1, the spray drift distance is 26 feet.

206

207

208

209 Figure 1. Example calculation of the terrestrial spray drift distance using the target 

210 “Fraction of Applied” as the input for a ground application. The inputs are “Point 

211 Deposition” and the “Fraction of Applied.” The output is the “Distance to Point or Area 

212 Average from Edge of Field,” and it represents the terrestrial spray drift distance. In this 

213 calculation, the spray drift distance is 26 feet.

214

215 Terrestrial Plants: Under Terrestrial Assessment, select “Point Deposition,” input the maximum 

216 single application rate in pounds active ingredient per acre into the “Active Rate” and the 

217 appropriate toxicity endpoint into “lb/ac” under “Initial Average Deposition” for ground and 

218 aerial applications and click on “Calc.” Figure 2 is a screenshot from AgDRIFT using this 

219 method. This assessment does not consider spray drift deposition from multiple applications. 

 17 This calculation applies to sublethal effects that do not have a corresponding LOC, such as acute sublethal effects. 

There are some chronic growth and reproductive endpoints for which the chronic LOC of one is commonly used.
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220 The EC25 values for the most sensitive tested monocot and dicot species from either seedling 

221 emergence or vegetative vigor tests are used to define the toxicity of the pesticide for non-listed 

222 species. 

223

224

225 Figure 2. Example calculation of the terrestrial spray drift distance using the “Active 

226 Rate” and “Initial Average Deposition” in “lb/ac” as the input. The output is the “Distance 

227 to Point or Area Average from Edge of Field,” and it represents the terrestrial spray drift 

228 distance. In this calculation, the spray drift distance is 26 feet.

229

230 2.3. Modeling Exposure to Aquatic Organisms Off the Field

231

232 Aquatic model scenarios run without spray drift represent aquatic concentrations due to runoff 

233 only, e.g., assuming no drift due to spray drift buffer setback. Comparing concentrations with 

234 and without drift gives an estimate of the contribution of drift to aquatic concentrations and 

235 information on whether a buffer may be used to mitigate risk to aquatic organisms. The relative 

236 importance of runoff and drift in PRZM/EXAMS scenarios is dependent on application 

237 parameters, the climatic conditions of the scenario and the timing of application. Table 1 

238 provides an example of the percentage of the exposure estimates due to spray drift for one 

239 chemical for a set of California sites. Runoff accounted for a wide range of the total estimated 

240 environmental concentrations (EEC). For example, runoff accounted for a high percentage of 
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241 the EEC in the forestry and nursery scenarios (71 – 98%) and a very low percentage of the EEC 

242 for the fruit and melon scenarios (2 –12%). 

243

244 Table 1. Estimated amount of the EEC that is due to runoff (the higher the percentage the 

245 less the EEC was influenced by spray drift)*

Scenario

Runoff-only (EECs) /Runoff plus Drift EECs (Percent)

Peak 21 Day 60 Day

CAnurserySTD 98% 90% 85%

CAColeCropRLF 81% 52% 44%

CAcotton_WirrigSTD 66% 38% 32%

CAtomato_WirrigSTD 30% 11% 9%

CA almond WirrigSTD 26% 17% 20%

CAfruit_WirrigSTD 12% 6% 5%

CAMelonsRLF 6% 3% 2%

246 *All model runs involved the same compound and same input parameters, except for spray drift. When drift was 

247 included in the scenario, the drift fraction was assumed to be 0.01 or 0.05, depending on whether an aerial or ground 

248 application was modeled. These percentages would be different if these default values were not used.

249

250 One important caveat for this analysis is that the spray drift analysis should also include an 

251 evaluation of the most sensitive toxicological endpoint. Even for scenarios where runoff 

252 contributes substantially to an EEC, a highly sensitive taxa with a low toxicity endpoint (e.g., 

253 having a high toxicity) could yield a large spray drift buffer for mitigating exposure to spray 

254 drift. The aquatic spray drift distance could result in a greater spray drift distance than the 

255 terrestrial spray drift distance. Therefore, if LOCs are exceeded, a spray drift distance may be 

256 calculated regardless of whether runoff or spray drift are driving aquatic EECs. 

257

258 In general, buffers that are vegetated and well maintained to prevent channelized flow have been 

259 shown to be best for reducing pesticide loading. The document titled “Conservation Buffers to 

260 Reduce Pesticide Losses” describes how to maintain buffers in a manner to prevent concentrated 

261 flow and to maximize pesticide trapping (USDA, 2000). The Agency does not currently have an 

262 approved tool to model the impact of various buffer distances and types on runoff loading. If 

263 channelized flow occurs in buffers, pesticide loadings in runoff to a water body can be 

264 significant. Additionally, many agricultural areas and golf courses have installed drainage that 

265 flows directly into water bodies (Wright and Sands 2001; Haith and Rossi 2003). 

266 2.3.a Estimating the Aquatic Spray Drift Fraction for Use in PRZM/EXAMS

267 at a Specified Distance from the Edge of the Field

268

269 When estimating aquatic exposure using PRZM/EXAMS, estimate the spray drift fraction using 

270 AgDRIFT, starting with deposition at zero feet from the edge of the field. For ecological risk 

271 assessments, the “EPA Defined Pond” is used as the water body in AgDRIFT. Appendix B 

272 provides instructions for estimating the spray drift fraction using AgDRIFT and provides tables 

273 of the spray drift fraction for different distances for the “EPA Defined Pond,” which is used to 
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274 estimate aquatic exposure in ecological risk assessments. For drinking water assessments, the 

spray drift fraction is calculated as specified in Appendix C.

18 275 The Application Efficiency is 

276 0.95 for all aerial applications and 0.99 for all ground applications, including orchard airblast 

applications, regardless of the spray drift fraction.19 277 For granular applications and other 

278 applications methods, EFED assumes negligible drift; therefore, the spray drift and application 

279 efficiency should be set to 0.00 and 1.0, respectively. Table 2 provides example spray drift 

280 inputs at zero feet from the edge of the field using AgDRIFT Tier I default assumptions. All 

281 other input parameters should follow the Guidance for Selecting Input Parameters in Modeling 

the Environmental Fate and Transport of Pesticides20 282 .

283

284 Table 2. PRZM/EXAMS Default and Additional Inputs for Percent of Spray Drift for 

285 Applications of Liquids without Any Spray Drift Limitations (Estimated Using AgDRIFT 

286 Version 2.1.1)

Type of Application Drop Size Distribution (DSD) Percent of Spray Drift for Runoff 

and Drift EEC without Bufferd

Ecological Risk Assessment Using EPA Farm Pond

Aerial 

Very Fine to Fine 24.2

Fine to Medium (default)c 12.5

Medium to Coarse 8.9

Coarse to Very Coarse 6.8

Ground (High boom)1 Very Fine to Fine (default)c 6.2

Ground (Low boom) 1 Very Fine to Fine 2.7

Ground (High boom) 1 Fine to Medium/Coarse 1.7

Ground (Low boom) 1 Fine to Medium/Coarse 1.1

Airblast (Sparse: young , dormant) Aerosol to Very Finec 4.2a

Airblast (Dense) Aerosol to Very Fine 1.5b

Airblast (Vineyard) Aerosol to Very Fine 0.2b

Airblast (Orchard) Aerosol to Very Fine 2.2b

Drinking Water Assessments Using Index Reservoirb

Aerial 

Very Fine to Fine 25.8

Fine to Medium (default)c 13.5

Medium to Coarse 9.7

Coarse to Very Coarse 7.6

Ground (High boom) Very Fine to Fine (default)c 6.6

Ground (Low boom) Very Fine to Fine 2.7

Ground (High boom) Fine to Medium/Coarse 1.7

Ground (Low boom) Fine to Medium/Coarse 1.1

Airblast (Sparse: young , dormant) Aerosol to Very Finec 4.8b

Airblast (Dense) Aerosol to Very Fine 1.7b

Airblast (Vineyard) Aerosol to Very Fine 0.3

Airblast (Orchard) Aerosol to Very Fine 2.5

a This is a 50th 287 percentile drift estimate and is not a conservative (high-end) estimate of possible exposure.

288 b Estimated using calculations shown in Appendix C.

 18 An example of these calculations is shown in Appendix C for 15 mph wind speeds, a limitation commonly 

observed on labels.

19 The spray drift fraction is a fraction of the application rate, while the application efficiency is the fraction of the 

total applied that reaches the field. These fractions are not expected to sum to a value of one. 20 U.S. EPA 2009. Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of 

Pesticides. Version 2.1 October 22, 2009. Environmental Fate and Effects Division. Office of Pesticide Programs. 

Available at: http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm
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289 c This is a default input for estimating exposure in the Environmental Fate and Effects Division. The default is used 

290 in exposure modeling unless there is a reason to deviate from the default assumption.

291 d These defaults are based on the current model of AgDRIFT 2.1.1. These defaults should be updated as the model 

292 is updated.

293

294 2.3.b Estimating the Aquatic Spray Drift Distance

295

296 The following steps explain how to determine whether spray drift is an important component of 

297 the estimated aquatic exposure and how a spray drift distance is estimated for aquatic organisms. 

298

299 1. Determine PRZM/EXAMS EECs with drift fractions, as described in Section 2.3.a.

300

301 2. Determine whether to estimate a spray drift distance. Figure 3 is a flow chart that gives an 

302 overview of when to determine the aquatic spray drift distance. The following points should 

303 be considered:

304

305 a. If the PRZM/EXAMS EEC resulting from both runoff and drift does not result in aquatic 

306 LOC exceedances, then no additional spray drift analysis is needed. 

307

308 b. If there are LOC exceedances, determine PRZM/EXAMS EECs without drift (e.g., the 

309 spray drift efficiency is set to 0). If the runoff only EEC from PRZM/EXAMS results in 

310 LOC exceedances, reducing spray drift will not mitigate the risk as estimated by 

311 PRZM/EXAMS. When discussing the impact of a spray drift buffer to the risk manager, 

312 indicate that while a spray drift buffer will not mitigate risk it will reduce risk. Estimate a 

313 spray drift distance looking at exposure to spray drift alone using AgDRIFT and only 

314 considering acute risk as specified in Section 4a on Page 16. This analysis provides 

315 information on whether acute exposure to spray drift alone could result in risk.

316

317 c. If there are LOC exceedances when both runoff and spray drift are considered and no 

318 LOC exceedances for runoff only EECs, estimate a spray drift distance, as described in 

319 Section 4b on Page 17, using AgDRIFT and PRZM/EXAMS. Also estimate a spray drift 

320 distance looking at exposure to spray drift alone, using AgDRIFT and only considering 

321 acute risk as described in Section 4a on Page 16. This analysis provides information on 

322 whether acute exposure to spray drift alone could result in risk.

323

324
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325

326

327 Figure 3. Flow Chart on When to Determine the Aquatic Spray Drift Distance

328

329

330

Determine PRZM/EXAMs 

EECs without drift

a. Do not calculate a 

spray drift distance 

because there is no risk

c. Calculate a spray drift distance 

that considers risk due to exposure 

to both runoff and spray drift as 

described in Section 4b on Page 

17. Estimate a spray drift distance 

as described in Section 4a on Page 

16.

Runoff only EEC does not result 

in LOC exceedance, but the EEC 

that considers both drift and 

runoff does result in an LOC 

exceedance

No LOC Exceedance

Runoff Only EEC 

Results in LOC exceedance

b. Risk cannot be mitigated using 

a spray drift buffer; however, any 

buffer used will help reduce risk. 

Estimate a spray drift distance 

using Section 4a on Page 16.

Determine PRZM/EXAMS EECS 

with Drift 

Calculate RQs and 

Compare to LOCs

LOC Exceedance
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331 3. When appropriate, calculate the ratio of runoff-only EEC to the runoff plus drift EEC. A 

332 qualitative evaluation of the relative importance of drift to total loading can be made, but no 

333 quantitative criteria exist to determine how important drift is for a given chemical and use 

334 setting.

335

336 Fraction of EEC due to Runoff = Runoff-only EEC / Runoff plus Drift EEC

337

338 This information may be used in the characterization of exposure and in explaining the results. 

339

340 4. An aquatic spray drift distance may be calculated by only considering spray drift and acute 

341 exposure using AgDRIFT, described under Section a below and by considering acute and 

342 chronic exposure to both runoff and spray drift using PRZM/EXAMS and AgDRIFT

343 (described under Section b below). 

344

345 a. To calculate the aquatic spray drift distance that considers only exposure to spray drift 

346 from a single application and acute risk to aquatic organisms, run AgDRIFT as described 

347 in Section 2.1. Under the “Toolbox” menu, choose “Aquatic Assessment.” Select “EPA348 Defined Pond” and input the target “Initial Average Concentration.” The initial average 

349 concentration is defined by AgDRIFT as “the average concentration within a defined 

350 water body, in nanograms per liter or parts per trillion.” Therefore, the input for initial 

351 average concentration is the concentration in water that will not result in an LOC 

352 exceedance. Figure 4 shows the inputs and outputs in AgDRIFT. 

353

354 Aquatic Animals:

355 Target initiation average concentration = LC50 × LOC

356 Aquatic plants:

357 Target initial average concentration = EC50 (for non-listed plants) 

358

359 The following is an example of spray drift distance calculations considering 

360 exposure spray drift only (e.g., excluding runoff) from a single application. The 

361 example would apply to a label that specified use of a very fine to fine DSD. 

362

363 Tier I, Aerial Application, Very Fine to Fine DSD

364 Application Rate = 0.25 lbs a.i./A

365 Non-listed Species LOC = 0.5

366 LC50 = 4 μg/L

367

368 Estimated spray drift distance for an aquatic animal based on spray drift only

369

370 Initial Average Concentration = LC50 × LOC 

371 = 4 μg/L × 0.5 = 2 μg/L or 2000 ng/L

372

373 The estimated spray drift distance is 105 feet. 

374
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375

376 Figure 4. Example calculation of the aquatic spray drift distance using the “Active Rate” 

377 and “Initial Average Concentration” as inputs. The output is the “Distance to Point or 

378 Area Average from Edge of Field.” In this calculation, the spray drift distance is 105 feet.

379

380

381 b. To estimate the spray drift distance considering exposure to both runoff and spray drift,

382 use PRZM/EXAMS to find a spray drift fraction that mitigates risk and then use 

383 AgDRIFT to find the corresponding spray drift distance. Using trial and error, change 

384 the spray drift fraction input in PRZM/EXAMS and find a value that will mitigate risk to 

385 both acute and chronic exposures. Once you find the spray drift fraction that will 

386 mitigate risk, use AgDRIFT to find the corresponding buffer distance to the identified 

387 spray drift fraction. To do this, open AgDRIFT and under the “Toolbox” menu, choose 

388 “Aquatic Assessment.” Select “EPA-Defined Pond” and input the spray drift fraction 

389 that will mitigate risk into the “Fraction of Applied.” The output will be “Distance to the 

390 Water Body from Edge of Field, which will mitigate risk to aquatic organisms.

391

392 5. Round all spray drift distances to a whole number. Report all inputs and outputs used for 

393 modeling in the risk assessment.

Select

Input

Input

Output: Aquatic 

Spray Drift Distance
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394 2.4. Reporting on Modeling Procedures, Results, and Uncertainties

395

396 This section provides some example language that may be used to discuss both aquatic and 

397 terrestrial spray drift distances. The purpose of the language is to provide an example discussion 

398 of the uncertainty involving one and multiple applications and involving a situation where a 

399 greater than value occurs for a spray drift distance. The language is very basic and should be 

400 edited as needed to summarize the spray drift distance results in an assessment, especially with 

401 regard to direct and indirect effects. Tables 3 and 4 show some example results for terrestrial 

402 spray drift distances. In the example, the maximum spray drift distance would be greater than 

403 997 feet. 

404

405 Table X shows the spray drift distances estimated using LOCs divided by risk quotients 

406 (calculated based on multiple applications) as the “Fraction of Applied” in AgDRIFT to 

estimate the spray drift distance for terrestrial animals. Based on AgDRIFT21 407 , potential direct 

408 effects from exposure to spray drift may occur at greater than 997 feet from the use site for 

409 multiple applications. 

410

411 The distance estimated for plants is based on one application and does not reflect possible 

412 cumulative exposure from multiple applications. It is recognized that a species could receive 

413 exposure from multiple applications, in which case, this distance may underestimate risk. The 

414 distance estimated for aquatic and terrestrial animals for multiple applications may occur when 

415 wind is blowing consistently in one direction for all applications or when wind is blowing in 

416 different directions during different applications as long as the organism is downwind in each 

417 case and regardless of whether it is mobile or stationary. This may result in an overestimation 

418 of exposure for aquatic and terrestrial organisms whose spray drift distances are based on 

419 exposure to the maximum number of applications and who are not downwind of every 

420 application. Exposure to multiple applications is more likely to occur when agricultural 

421 fields/use areas are on multiple sides of an aquatic or terrestrial area of interest and when local 

422 wind direction is not variable. 

423

424 Table 3. Example of Spray Drift Distances Calculated for Terrestrial Animals, Assuming 

425 Aerial Application*

Taxa Type of 

Endpoint

Highest Risk 

Quotient LOC** Fraction of Applied 

= LOC/RQ

Spray Drift Distance

(feet)

Birds

Acute 25 0.5 0.02 479

Chronic 6.9 1 0.14 69

Mammals

Acute 16.7 0.5 0.03 312

Chronic 136.23 1 0.01 >997

426 RQ=risk quotient

427 * A spray drift estimation of zero may result when the highest RQ exceeds the LOC because the model used to 

428 estimate spray drift exposure is a different model from the model used to estimate terrestrial EECs. In this case, the 

429 spray drift distance needed to mitigate risk is expected to be very small. 

430 **The LOCs shown are for non-listed species. 

431

 21 Modeled using the following input parameters for AgDRIFT: maximum application rate, Tier I Terrestrial 

Assessment, aerial application, ASAE Fine to Medium DSD, and assuming a single application.
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432 Table 4. Example of Spray Drift Distance for Non-listed Terrestrial Plants 

Taxa EC25(lbs 

ai/A)

Maximum Application 

Rate in (lbs ai/A)

Spray Drift Distance for One 

Application (feet)

Terrestrial 

Plants 0.0067 4 >997

433

434 Literature Cited

435

436 Haith, D. A. and F. S. Rossi. 2003. Risk assessment of pesticide runoff from turf. Journal of 

437 Environmental Quality 32: 447-455.

438

439 National Academy of Sciences. 2013. Assessing Risks to Endangered and Threatened Species 

440 from Pesticides. The National Academies Press. Washington DC. Available at 

441 http://www.nap.edu/catalog.php?record_id=18344 (Accessed September 26, 2013).

442

443 USDA, NRCS. 2000. Conservation Buffers to Reduce Pesticide Losses. March 2000. Natural 

444 Resources Conservation Service. United States Department of Agriculture. Fort Worth, 

445 TX. Available at http://www.in.nrcs.usda.gov/technical/agronomy/newconbuf.pdf

446 (Accessed May 28, 2013).

447

448 Wright, J., & Sands, G. 2001. Planning an Agricultural Subsurface Drainage System. BU449 07685. 2009. Agricultural Drainage Publication Series: Soil Water Concepts. 

450 University of Minnesota. Available at 

451 http://www.extension.umn.edu/distribution/cropsystems/DC7685.html (Accessed 

452 October 28, 2010).

453

454
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Appendix A. Comparison of Results from Tier I, Tier II, and Tier III AgDRIFT Analysis Using the ASAE Very Fine to Fine 

DSD and Fine to Medium DSD

Table A1. Comparison of the Distances from Edge of Field to Point Downwind from Tier I, Tier II, and Tier III AgDRIFT 

Terrestrial Assessments Using the Default Input Parameters Specified in Section 2.1 and the Specified DSD

Fraction of 

Applied 

Deposited at 

Point 

Downwind

Spray Drift Distance (Feet)

ASAE Very Fine to Fine DSD ASAE Fine to Medium DSD

Tier I Tier II Tier II÷ 

Tier I Tier III Tier III÷ Tier I Tier I Tier II Tier II÷ Tier I Tier III Tier III÷ Tier I

0.01 Out of 

Range

Out of 

Range na na na

Out of 

Range

Out of 

Range na 1387.78 na

0.02 Out of 

Range

Out of 

Range na na na 479 479 1.00 479 1.00

0.03 Out of 

Range

Out of 

Range na na na 311.68 311.68 1.00 314.96 1.01

0.04 Out of 

range

Out of 

Range na 1076.1 na 236.22 232.94 0.99 236.22 1.00

0.05 741.46 708.65 0.96 741.46 1.00 183.72 183.72 1.00 187.01 1.02

0.06 577.42 557.74 0.97 577.42 1.00 160.76 160.76 1.00 160.76 1.00

0.08 400.26 390.42 0.98 400.26 1.00 121.39 121.39 1.00 121.39 1.00

0.1 305.11 295.27 0.97 305.11 1.00 98.42 98.42 1.00 98.42 1.00

0.2 124.67 121.39 0.97 124.67 1.00 32.81 32.81 1.00 32.81 1.00

0.3 52 52.49 1.01 52.49 1.01 16.4 16.4 1.00 16.4 1.00

0.4 16 13.12 0.82 16.4 1.03 6.56 6.56 1.00 6.56 1.00

0.5 3 0 0.00 3.28 1.09 0 3.28 na 0 na

0.6 0 0 na na 0 0 na 0 na

na=not applicable
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Table A2. Comparison of Distances from Edge of Field to Water Body from Tier I, Tier II, and Tier III AgDRIFT Aquatic 

Assessments Using the Default Input Parameters Specified in Section 2.1 and the Specified DSD

Initial Average 

Concentration (ng/L) 

in Water Body with 

Active Rate of 0.2505

Spray Drift Distance to Water Body (Feet)

Very Fine to Fine DSD Fine to Medium DSD

Tier I Tier II Tier II÷ 

Tier I Tier III

Tier 

III÷ 

Tier I

Tier I Tier II Tier II÷ 

Tier I Tier III

Tier 

III÷ 

Tier I

3300 7 3 0.5 7 1 0 0 na 0 na

3000 23 20 0.86 23 1 0 0 na 0 na

2000 105 102 0.97 108 1.03 0 0 na 0 na

1000 367 354 0.96 367 1 55.77 55.77 1.00 55.77 1.00

950 397 381 0.96 400 1.01 62.34 62.34 1.00 62.34 1.00

800 522 499 0.96 522 1 85.3 85.3 1.00 85.3 1.00

700 646 617 0.95 646 1 104.99 104.99 1.00 104.99 1.00

600 850 804 0.95 853 1 134.51 131.23 0.98 134.51 1.00

556 994 938 0.94 1001 1.01 150.92 147.64 0.98 147.64 0.98

550 Out of 

range

955 na 1020 na 150.92 150.92 1.00 150.92 1.00

540 Out of 

range

994 na 1063 na 154.2 154.2 1.00 154.2 1.00

530 Out of 

range

Out of 

range

na 1106 na 160.76 157.48 0.98 160.76 1.00

257 Out of 

range

Out of 

range

Out of 

range

2605 na 433.07 423.22 0.98 433.07 1.00

200 na na na na na 623.35 610.23 0.98 626.63 1.01

157 na na na na na 990.8 967.84 0.98 997.36 1.01

156 na na na na na

Out of 

Range 980.96 na 1010.49 na

155 na na na na na

Out of 

Range 994.08 na 1026.89 na

154 na na na na na

Out of 

Range

Out of 

Range 1043.29 na
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Initial Average 

Concentration (ng/L) 

in Water Body with 

Active Rate of 0.2505

Spray Drift Distance to Water Body (Feet)

Very Fine to Fine DSD Fine to Medium DSD

Tier I Tier II Tier II÷ 

Tier I Tier III

Tier 

III÷ 

Tier I

Tier I Tier II Tier II÷ 

Tier I Tier III

Tier 

III÷ 

Tier I

100 na na na na na

Out of 

Range

Out of 

Range 1952.08 na

64 na na na na na

Out of 

Range

Out of 

Range 2595.11 na

63 na na na na na

Out of 

Range

Out of 

Range

Out of 

Range na

na=not applicable
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Appendix B. How to Determine the Aquatic and Terrestrial Spray Drift Fraction for an

Application Rate in AgDRIFT for Ecological Assessments

1. Select the default input parameters for Tier I analysis as described in Section 2.1.

2. Select "Tool box" and then "Aquatic Assessment" or “Terrestrial Assessment”. 

3. Select the appropriate water body from the following choices: 

For an aquatic assessment, select:

a. “EPA-Defined Pond”: Pond with a depth of 2 meters (6.56 ft) and a downwind 

width of 63.61 m (208.69 ft) and flight line width of 157.21 m (515.78 ft for a 1 

ha pond).

For a terrestrial assessment, select point deposition.

4. Enter the maximum application rate for the use being evaluated in the "Active Rate" 

window. This input does not change the fraction of applied pesticide distributed to the 

water body. 

5. Enter a “Distance to Point or Water Body from Edge of Field” (Figure B1). If a distance 

is not specified on the label, the “Distance to the Point of Water Body from the Edge of 

Field” is zero for aquatic ecological risk assessments and one foot for terrestrial 

assessments. For Drinking Water Assessments, see Appendix C. Click the “Calc”

button. The model then reports the “Fraction of Applied,” which is the estimated spray 

drift fraction or fraction of pesticide application rate that will enter the water body or will 

be deposited at a point off the field for a terrestrial assessment.1 Tables B1-B6 provide 

some example outputs for standard spray drift fractions associated with different 

distances. 
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Figure B1. Example of the AgDRIFT input and output screen used to determine the spray 

drift fraction. The input is the “Distance to Water Body from Edge of Field” shown in red 

and the output is the “Fraction of Applied” or spray drift fraction.

Table B1. Fraction of Applied Pesticide at Different Distances from the Edge of the Field 

to the Water Body that will be Distributed into the EPA Pond with Ground Application

(Calculated using Tier I Model in AgDRIFT version 2.1.1)

Distance from Edge of 

Field to Water Body 

(feet)

Fraction of Applied or Spray Drift Fraction

High Boom Low Boom

ASAE Very 

Fine to Fine

ASAE Fine to 

Medium/Coarse

ASAE Very 

Fine to Fine

ASAE Fine to 

Medium/Coarse

0 0.0616 0.0165 0.0268 0.0109

1 0.0572 0.0137 0.0231 0.0086

5 0.0455 0.0104 0.0167 0.0065

10 0.0376 0.009 0.0136 0.0056

25 0.0267 0.0071 0.01 0.0045

50 0.0194 0.0056 0.0076 0.0036

100 0.013 0.0042 0.0054 0.0028

150 0.0098 0.0034 0.0043 0.0023

200 0.0078 0.0028 0.0036 0.0019

250 0.0064 0.0024 0.0031 0.0017

300 0.0053 0.0021 0.0027 0.0015

350 0.0046 0.0019 0.0024 0.0013

400 0.0039 0.0017 0.0021 0.0012

450 0.0035 0.0015 0.0019 0.0011

Input

Output: Fraction 

Spray Drift

Select
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Distance from Edge of 

Field to Water Body 

(feet)

Fraction of Applied or Spray Drift Fraction

High Boom Low Boom

ASAE Very 

Fine to Fine

ASAE Fine to 

Medium/Coarse

ASAE Very 

Fine to Fine

ASAE Fine to 

Medium/Coarse

500 0.003 0.0014 0.0017 0.001

550 0.0027 0.0013 0.0016 0.0009

600 0.0024 0.0012 0.0015 0.0009

650 0.0022 0.0011 0.0013 0.0008

700 0.002 0.001 0.0012 0.0008

750 0.0018 0.0009 0.0012 0.0007

800 0.0017 0.0009 0.0011 0.0007

850 0.0015 0.0008 0.001 0.0006

900 0.0014 0.0008 0.001 0.0006

950 0.0013 0.0007 0.0009 0.0006

997 0.0012 0.0007 0.0009 0.0006

998 Out of range Out of range Out of range Out of range

Table B3. Fraction of Applied Pesticide at Different Distances from the Edge of the Field 

to the Water Body that will be Distributed into the EPA Pond with Aerial Application

(Calculated Using Tier I Model in AgDRIFT Version 2.1.1)

Distance from Edge of Field 

to the Water Body (feet)

Fraction of Applied or Spray Drift Fraction

ASAE Very Fine to Fine ASAE Fine to 

Medium

ASAE Medium to 

Coarse

0 0.2421 0.1254 0.0885

1 0.2405 0.1276 0.0866

5 0.2340 0.116 0.0789

10 0.2266 0.1082 0.0713

25 0.2076 0.0916 0.0564

50 0.1821 0.0733 0.0428

100 0.1446 0.0503 0.0271

150 0.1196 0.0385 0.0197

200 0.1023 0.0314 0.0154

250 0.0889 0.0266 0.0126

300 0.0804 0.0231 0.0108

350 0.0730 0.0205 0.0095

400 0.0670 0.0186 0.0086

450 0.0622 0.0172 0.0081

500 0.0582 0.016 0.0074

550 0.0549 0.015 0.007

600 0.052 0.0144 0.0066

650 0.0495 0.0138 0.0063

700 0.0474 0.0132 0.0061

750 0.0455 0.0128 0.0058

800 0.0439 0.0124 0.0056

850 0.0425 0.012 0.0055

900 0.0412 0.0117 0.0053

950 0.0401 0.0114 0.0052

997 0.0392 0.0111 0.0051
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Distance from Edge of Field 

to the Water Body (feet)

Fraction of Applied or Spray Drift Fraction

ASAE Very Fine to Fine ASAE Fine to 

Medium

ASAE Medium to 

Coarse

998 Out of range Out of range Out of range

Table B4. Fraction of Applied Pesticide at Different Distances from the Edge of the Field 

to a Terrestrial Point with Aerial Application (Calculated Using Tier I Model in AgDRIFT 

Version 2.01)

Distance from Edge of Field 

to Terrestrial Point

Fraction of Applied or Spray Drift Fraction

ASAE Very Fine to 

Fine

ASAE Fine to 

Medium

ASAE Medium to 

Coarse

0 0.5001 0.5 0.5

1 0.4916 0.4808 0.4768

5 0.4572 0.4 0.3842

10 0.4234 0.3347 0.3

25 0.361 0.2207 0.1698

50 0.3011 0.1709 0.1108

100 0.2236 0.0978 0.0572

150 0.1756 0.0627 0.0345

200 0.1401 0.0456 0.0245

250 0.1159 0.0367 0.0184

300 0.1001 0.0306 0.0146

350 0.0886 0.026 0.0122

400 0.0796 0.0227 0.0106

450 0.0725 0.0203 0.0094

500 0.0666 0.0185 0.0085

550 0.0621 0.0171 0.0079

600 0.0583 0.016 0.0074

650 0.0548 0.0151 0.007

700 0.0518 0.0146 0.0066

750 0.0494 0.0137 0.0063

800 0.0474 0.0132 0.006

850 0.0455 0.0128 0.0058

900 0.0439 0.0124 0.0057

950 0.0425 0.012 0.0055

997 0.0413 0.0117 0.0053

998 Out of range Out of range Out of range

Table B5. Fraction of Applied Pesticide at Different Distances from the Edge of the Field 

to a Terrestrial Point with Ground Application with a High Boom (Calculated Using Tier I 

Model in AgDRIFT Version 2.1.1)

Distance from Edge of Field to 

Terrestrial Point (feet)

Fraction of Applied or Spray Drift Fraction

ASAE Very Fine to 

Fine

ASAE Fine to 

Medium/Coarse

0 1.06 1.01

1 0.8564 0.3731
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Distance from Edge of Field to 

Terrestrial Point (feet)

Fraction of Applied or Spray Drift Fraction

ASAE Very Fine to 

Fine

ASAE Fine to 

Medium/Coarse

5 0.4475 0.0889

10 0.2595 0.0459

25 0.104 0.0208

50 0.05 0.0119

100 0.0248 0.007

150 0.0164 0.0051

200 0.012 0.004

250 0.0093 0.0033

300 0.0075 0.0028

350 0.0062 0.0024

400 0.0053 0.0021

450 0.0045 0.0019

500 0.0039 0.0017

550 0.0034 0.0015

600 0.003 0.0014

650 0.0027 0.0013

700 0.0024 0.0012

750 0.0022 0.0011

800 0.002 0.001

850 0.0018 0.0009

900 0.0017 0.0009

950 0.0015 0.0008

997 0.0014 0.0008

998 Out of range Out of range

Table B6. Fraction of Applied Pesticide at Different Distances from the Edge of the Field 

to a EPA Pond with Airblast Application (Calculated Using Tier I Model in AgDRIFT 

Version 2.01)

Distance from edge 

of field to water 

body (feet)

Fraction of Applied or Spray Drift Fraction

Normal (Stone and 

Pome Fruit, 

Vineyard)

Dense 

(Citrus, Tall 

Trees)

Sparse 

(Young, 

Dormant)

Vineyard Orchard

0 0.0011 0.0145 0.0416 0.0024 0.0218

1 0.0011 0.014 0.0395 0.0023 0.0208

5 0.001 0.0122 0.0323 0.0018 0.0175

10 0.0009 0.0106 0.0258 0.0014 0.0145

25 0.0007 0.0074 0.015 0.0009 0.0093

50 0.0005 0.005 0.0077 0.0006 0.0056

100 0.0003 0.003 0.0031 0.0003 0.0031

150 0.0002 0.0022 0.0017 0.0002 0.0021

200 0.0002 0.0017 0.001 0.0002 0.0016

250 0.0002 0.0014 0.0007 0.0001 0.0013

300 0.0001 0.0012 0.0005 0.0001 0.0011

350 0.0001 0.0011 0.0004 0.0001 0.0009
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400 0.0000978 0.001 0.0003 0.0000881 0.0008

450 0.0000863 0.0009 0.0002 0.0000765 0.0007

500 0.0000769 0.0008 0.0002 0.0000672 0.0007

550 0.0000629 0.0007 0.0002 0.0000596 0.0006

600 0.0000626 0.0007 0.0001 0.0000533 0.0005

650 0.0000571 0.0006 0.0001 0.000048 0.0005

700 0.0000523 0.0006 0.0000898 0.0000435 0.0005

750 0.0000482 0.0005 0.0000771 0.0000397 0.0004

800 0.0000446 0.0005 0.0000668 0.0000363 0.0004

850 0.0000414 0.0005 0.0000583 0.0000334 0.0004

900 0.0000386 0.0005 0.0000513 0.0000309 0.0004

950 0.0000361 0.0004 0.0000453 0.0000286 0.0003

997 0.0000339 0.0004 0.0000405 0.0000267 0.0003

998 Out of Range Out of Range

Out of 

Range Out of Range

Out of 

Range

Table B7. Fraction of Applied Pesticide at Different Distances from the Edge of the Field 

to a Terrestrial Point with Airblast Application (Calculated Using Tier I Model in 

AgDRIFT Version 2.1.1)

Distance from edge of 

field to water body (feet)

Fraction of Applied or Spray Drift Fraction

Normal (Stone 

and Pome 

Fruit, 

Vineyard)

Dense 

(Citrus, Tall 

Trees)

Sparse 

(Young, 

Dormant)

Vineyard Orchard

0 0.0089 0.1155 0.4763 0.0376 0.2223

1 0.0081 0.1078 0.4385 0.0324 0.2046

5 0.0058 0.0834 0.3218 0.0195 0.1506

10 0.0042 0.0631 0.2285 0.012 0.108

25 0.0023 0.033 0.1007 0.0047 0.0503

50 0.0012 0.0157 0.0373 0.0019 0.021

100 0.0006 0.0065 0.0103 0.0008 0.0074

150 0.0004 0.0038 0.0044 0.0004 0.004

200 0.0003 0.0026 0.0023 0.0003 0.0026

250 0.0002 0.002 0.0014 0.0002 0.0019

300 0.0002 0.0016 0.0009 0.0002 0.0015

350 0.0002 0.0014 0.0006 0.0001 0.0012

400 0.0001 0.0012 0.0005 0.0001 0.0011

450 0.0001 0.0011 0.0004 0.0001 0.0009

500 0.0000965 0.0009 0.0003 0.000087 0.0008

600 0.0000765 0.0008 0.0002 0.0000667 0.0006

700 0.0000625 0.0007 0.0001 0.0000531 0.0005

800 0.0000523 0.0006 0.0000889 0.0000434 0.0005

900 0.0000446 0.0005 0.0000665 0.0000363 0.0004

997 0.0000387 0.0005 0.0000514 0.000031 0.0004

998 Out of Range Out of Range

Out of 

Range Out of Range

Out of 

Range
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Appendix C. Calculation of the Spray Drift Fraction for Drinking Water Assessments 

Using the Index Reservoir.

The index reservoir scenario is used to model simulations to estimate drinking water exposure 

and is intended as a replacement of the “standard pond,” which is used to estimate wildlife 

exposure in aquatic ecosystems. The scenario is developed based on the Shipman City Lake in 

Shipman, Illinois. It includes ephemeral and perennial streams that run into a reservoir. For 

detailed information on use of the index reservoir in drinking water assessments, refer to 

Guidance on Development and Use of the Index Reservoir in Drinking Water (USEPA, 2010). 

The spray drift fraction for the index reservoir is calculated using AgDRIFT by adding the spray 

drift fraction of the reservoir (82-m width, 640-m length, 2.7-m average depth, no buffer ) to the 

spray drift fraction of all streams (4-m width, 1500-m length, variable depth, 4-m buffer) 

normalized to the index reservoir as follows:

Normalized Spray Drift Fraction for Streams (unitless) =

Surface Area of Reservoir

Surface Area of All Streams Spray Drift Fraction of all Streams ×

Adjusted Spray Drift Fraction for Index Reservoir (unitless) = 

Normalized Spray Drift Fraction for Streams + Spray Drift Fraction of Reservoir

Table C1 provides the estimated spray drift fraction of the application rate for the index reservoir

and the outputs from AgDRIFT used to make this calculation. At 10 mph wind speeds, the spray 

drift fraction of the application rate for the index reservoir is 14% for aerial applications, 7% for 

ground applications, and 14% for airblast applications, using the default spray drift inputs as 

specified in Section 2.1 and Tier I AgDRIFT version 2.1.1. The corresponding spray drift 

fraction at 15 mph wind speeds is 16% for aerial applications. 

Table C1. Estimate the Spray Drift Fraction for Drinking Water Assessments Using Tier I 

(10 mph wind speed) or Tier II (15 mph wind speed) Analysis in AgDRIFT Version 2.1.1

Scenario

Spray Drift Fraction Estimated from AgDRIFT Normalized Spray Drift Fraction

Aerial, Fine to 

Medium DSD1 Ground3,5 Airblast4 Aerial, Fine to Medium DSD1 Ground3,5 Airblast4

10 mph (4.47 m/s) Wind Speed

Reservoir 0.106 0.05 0.0326 0.106 0.05 0.0326

All Streams with 4-

m buffer 0.2531 0.1406 0.13537 0.0289 0.0161 0.0155

Index Reservoir 0.1349 0.0661 0.048

15 mph (6.71 m/s) Wind Speed

Reservoir 0.1537 NA5 NA5 0.1537 NA5 NA

All Streams with 4-

m buffer 0.408 NA5 NA5 0.0466 NA5 NA

Index Reservoir 0.2003 NA5 NA 1 Assumed Fine to Medium DSD. 2 Assumed Very Fine to Fine DSD. 3 Assumed Very Fine to Fine DSD, high boom, and 90th data percentile.
Draft for Comment

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4 Assumed sparse, young dormant orchard.

5 Ground and airblast applications are not adjusted for windspeed. 

USEPA. 2005. Clarification of Plant Evaluation Guidance. Memorandum From S. Bradbury to 

Environmental Fate and Effects Division. October 4, 2005. Office of Pesticide Programs. 

United States Environmental Protection Agency. 

USEPA. 2010. Guidance on Development and Use of the Index Reservoir in Drinking Water 

Exposure Assessments. September 14, 2010. Environmental Fate and Effects Division. 

Office of Pesticide Programs. United States Environmental Protection Agency. Available 

at http://www.epa.gov/oppefed1/models/water/index_reservoir_dwa.pdf (Accessed 

December 9, 2010).
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Version – November 1, 2013

29

Appendix D. Example and Validation of Terrestrial Spray Drift Distance Approach

Calculation of Risk Quotients (output from T-REX v 1.4.1)

Acute a 

Kenaga 

Chemical Name: The ma 

 Use both the 

 Formulation

Application Rate 1 lbs a.i./acre RQs re 

Half-life 35 days <0.01 i 

Application Interval 7 days figure 

Maximum # Apps./Year 5

Length of Simulation 1 year

Mallard duck LD50 (mg/kg-bw) 500.00

Bobwhite quail LC50 (mg/kg-diet) 200.00

Mallard duck NOAEL(mg/kg-bw) 10.00

Bobwhite quail NOAEC (mg/kg-diet) 10.00

500.00

200.00

10.00

10.00

Kenaga

Values

Short Grass 927.00

Tall Grass 424.88

Broadleaf plants/sm Insects 521.44

Fruits/pods/seeds/lg insects 57.94

 Upper Bound Kenaga Residues For RQ Calculation

Dietary-based EECs (ppm)

NOAEL (mg/kg-bw)

NOAEC (mg/kg-diet)

Mammals

LD50 (mg/kg-bw)

Chemical X

Corn

Product X

Endpoints

LC50 (mg/kg-diet)

Avian
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Avian Results

Avian Body Ingestion (Fdry) Ingestion (Fwet) % body wgt FI

Class Weight (g) (g bw/day) (g/day) consumed (kg-diet/day)

Small 20 5 23 114 2.28E-02

Mid 100 13 65 65 6.49E-02

Large 1000 58 291 29 2.91E-01

20 5 5 25 5.06E-03

Granivores 100 13 14 14 1.44E-02

1000 58 65 6 6.46E-02

Avian Body Adjusted LD50

Weight (g) (mg/kg-bw)

20 259.61

100 330.50

1000 466.84

small mid large

20 100 1000 20 100 1000

Short Grass 1055.76 602.04 269.54

Tall Grass 483.89 275.94 123.54

Broadleaf plants/sm Insects 593.87 338.65 151.62

Fruits/pods/seeds/lg insects 65.99 37.63 16.85 14.66 8.36 3.74

20 100 1000

Short Grass 4.07 1.82 0.58

Tall Grass 1.86 0.83 0.26

Broadleaf plants/sm insects 2.29 1.02 0.32

Fruits/pods/seeds/lg insects 0.25 0.11 0.04

Seeds (granivore) 0.06 0.03 0.01

Acute Chronic

Short Grass 4.64 92.70

Tall Grass 2.12 42.49

Broadleaf plants/sm Insects 2.61 52.14

Fruits/pods/seeds/lg insects 0.29 5.79

Avian Classes and Body Weights (grams) Dose-based EECs 

(mg/kg-bw) 

Granivores(grams)

Avian Acute RQs

Dose-based RQs Size Class (grams)

(Dose-based EEC/adjusted LD50)

Dietary-based RQs RQs

(Dietary-based EEC/LC50 or 

NOAEC)
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pp g 

Mammalian Results

Mammalian Body Ingestion (Fdry) Ingestion (Fwet) % body wgt FI

Class Weight (g bwt/day) (g/day) consumed (kg-diet/day)

15 3 14 95 1.43E-02

Herbivores/ 35 5 23 66 2.31E-02

insectivores 1000 31 153 15 1.53E-01

15 3 3 21 3.18E-03

Grainvores 35 5 5 15 5.13E-03

1000 31 34 3 3.40E-02

Mammalian Body Adjusted Adjusted

Class Weight LD50 NOAEL

15 1098.92 21.98

Herbivores/ 35 889.14 17.78

insectivores 1000 384.58 7.69

15 1098.92 21.98

Grainvores 35 889.14 17.78

1000 384.58 7.69

15 35 1000 15 35 1000

Short Grass 883.83 610.84 141.63

Tall Grass 405.09 279.97 64.91

Broadleaf plants/sm Insects 497.15 343.60 79.66

Fruits/pods/seeds/lg insects 55.24 38.18 8.85 12.28 8.48 1.97

15 grams 35 grams 1000 grams

Acute Chronic Acute Chronic Acute Chronic

Short Grass 0.80 40.21 0.69 34.35 0.37 18.41

Tall Grass 0.37 18.43 0.31 15.74 0.17 8.44

Broadleaf plants/sm insects 0.45 22.62 0.39 19.32 0.21 10.36

Fruits/pods/lg insects 0.05 2.51 0.04 2.15 0.02 1.15

Seeds (granivore) 0.01 0.56 0.01 0.48 0.01 0.26

Acute Chronic

Short Grass 4.64 92.70

Tall Grass 2.12 42.49

Broadleaf plants/sm insects 2.61 52.14

Fruits/pods/seeds/lg insects 0.29 5.79

Dose-based RQs 

(Dose-based EEC/LD50 or NOAEL)

Granivores(grams)

Mammalian Classes and Body weight

Dose-Based EECs 

(mg/kg-bw)

Herbivores/ insectivores (grams)

Dietary-based RQs 

(Dietary-based EEC/LC50 or 

NOAEC)

Mammal RQs

Small mammal Medium mammal Large mammal
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Table D1. Summary of the Calculation of Fraction of Applied.

Taxa Type of 

Endpoint Highest Risk Quotient LOC Fraction of Applied = 

LOC/RQ

Birds

Acute Oral 4.07 0.5 0.12

Acute Dietary 4.64 0.5 0.11

Chronic 92.70 1 0.011

Mammals

Acute Oral 0.80 0.5 0.625

Acute Dietary 4.64 0.5 0.11

Chronic 92.70 1 0.011

The spray drift distance that corresponds to 0.01 is out of range or greater than 997 feet. To verify that the fraction of applied would 

reduce the risk quotient to a value below LOCs, the Fraction of Applied is multiplied by the application rate and that is used as an 

input in T-REX. Note that all RQs are below LOCs in the T-REX output shown below. Also, note that this method will be applicable

to both single and multiple applications.
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Avian Results

Avian Body Ingestion (Fdry) Ingestion (Fwet) % body wgt FI

Class Weight (g) (g bw/day) (g/day) consumed (kg-diet/day)

Small 20 5 23 114 2.28E-02

Mid 100 13 65 65 6.49E-02

Large 1000 58 291 29 2.91E-01

20 5 5 25 5.06E-03

Granivores 100 13 14 14 1.44E-02

1000 58 65 6 6.46E-02

Avian Body Adjusted LD50

Weight (g) (mg/kg-bw)

20 259.61

100 330.50

1000 466.84

small mid large

20 100 1000 20 100 1000

Short Grass 10.56 6.02 2.70

Tall Grass 4.84 2.76 1.24

Broadleaf plants/sm Insects 5.94 3.39 1.52

Fruits/pods/seeds/lg insects 0.66 0.38 0.17 0.15 0.08 0.04

20 100 1000

Short Grass 0.04 0.02 0.01

Tall Grass 0.02 0.01 0.00

Broadleaf plants/sm insects 0.02 0.01 0.00

Fruits/pods/seeds/lg insects 0.00 0.00 0.00

Seeds (granivore) 0.00 0.00 0.00

Acute Chronic

Short Grass 0.05 0.93

Tall Grass 0.02 0.42

Broadleaf plants/sm Insects 0.03 0.52

Fruits/pods/seeds/lg insects 0.00 0.06

 

 

 

Avian Classes and Body Weights (grams)

 

Dose-based EECs 

(mg/kg-bw) 

Granivores(grams)

Avian Acute RQs

Dose-based RQs Size Class (grams)

(Dose-based EEC/adjusted LD50)

Dietary-based RQs RQs

(Dietary-based EEC/LC50 or 

NOAEC)
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pp g 

Mammalian Results

Mammalian Body Ingestion (Fdry) Ingestion (Fwet) % body wgt FI

Class Weight (g bwt/day) (g/day) consumed (kg-diet/day)

15 3 14 95 1.43E-02

Herbivores/ 35 5 23 66 2.31E-02

insectivores 1000 31 153 15 1.53E-01

15 3 3 21 3.18E-03

Grainvores 35 5 5 15 5.13E-03

1000 31 34 3 3.40E-02

Mammalian Body Adjusted Adjusted

Class Weight LD50 NOAEL

15 1098.92 21.98

Herbivores/ 35 889.14 17.78

insectivores 1000 384.58 7.69

15 1098.92 21.98

Grainvores 35 889.14 17.78

1000 384.58 7.69

15 35 1000 15 35 1000

Short Grass 8.84 6.11 1.42

Tall Grass 4.05 2.80 0.65

Broadleaf plants/sm Insects 4.97 3.44 0.80

Fruits/pods/seeds/lg insects 0.55 0.38 0.09 0.12 0.08 0.02

15 grams 35 grams 1000 grams

Acute Chronic Acute Chronic Acute Chronic

Short Grass 0.01 0.40 0.01 0.34 0.00 0.18

Tall Grass 0.00 0.18 0.00 0.16 0.00 0.08

Broadleaf plants/sm insects 0.00 0.23 0.00 0.19 0.00 0.10

Fruits/pods/lg insects 0.00 0.03 0.00 0.02 0.00 0.01

Seeds (granivore) 0.00 0.01 0.00 0.00 0.00 0.00

Acute Chronic

Short Grass 0.05 0.93

Tall Grass 0.02 0.42

Broadleaf plants/sm insects 0.03 0.52

Fruits/pods/seeds/lg insects 0.00 0.06

 

 

 

Dose-based RQs 

(Dose-based EEC/LD50 or NOAEL)

Granivores(grams)

Mammalian Classes and Body weight

Dose-Based EECs 

(mg/kg-bw)

Herbivores/ insectivores (grams)

Dietary-based RQs 

(Dietary-based EEC/LC50 or 

NOAEC)

Mammal RQs

Small mammal Medium mammal Large mammal