Draft for Comment

Version – November 1, 2013

Residential Exposure Assessment Standard 

Operating Procedures

Addenda 1: Consideration of Spray Drift

Office of Pesticide Programs

Office of Prevention, Pesticides, and Toxic Substances

U.S. Environmental Protection Agency

Washington, DC
U.S. EPA Office of Pesticide Programs – Residential Exposure Assessment Standard Operating Procedures, Addenda 1

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1 Table of Contents

2 Section 1 Introduction .............................................................................................. 2

3 Section 2 Problem Formulation............................................................................... 3

4 Section 3 Scoping....................................................................................................... 7

5 3.1 Information Gathering...................................................................................................................7

6 3.2 Scenario Development ..................................................................................................................8

7 3.2.1 Needs Screening .............................................................................................................. 8

8 3.2.2 Defining Scenarios .......................................................................................................... 9

9 3.2.3 Characterization of Spray Drift Potential ...................................................................... 11

10 Section 4 Method..................................................................................................... 12

11 4.1 Current Method In Residential SOPs For Calculating Dermal Exposure ...................................13

12 4.2 Modification To SOP Method To Account For Spray Drift .......................................................14

13 4.3 Drift Fraction Values...................................................................................................................14

14 Section 5 Considerations ........................................................................................ 18

15

16 Attachment A Derivation of Drift Fraction Estimates

17

18

19
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20 Section 1 Introduction

21 This document is as an addendum to the SOPs For Residential Exposure Assessment (hereafter 

SOPs)1 22 which was developed for the purpose of introducing procedures for assessing potential 

23 risks to human health associated with spray drift. This effort was undertaken to allow for routine 

24 consideration of these types of exposures in risk assessment, based on the current SOP for use of 

25 pesticides on turf, which is consistent with policy statements made by the Agency in a variety of 

forums.2 26 This document specifically provides guidance that defines when quantitative risk 

27 assessments for spray drift are required, and it also provides the information needed to complete 

such assessments when needed.3 28 Volatilization can also occur during or after application. This

29 document addresses only those exposures associated with spray drift and not volatilization.

30

31 Off-target movement of pesticides can occur via many types of pathways, and it is governed by a 

32 variety of factors. Sprays (or solid materials) that are released and do not deposit in the 

33 application area end up off-target and can lead to exposures through direct contact with sprays. It 

34 is also clear that incidents due to spray drift occur as noted in an analysis completed based on 

acute illnesses using 1998-2006 NIOSH SENSOR data.4 35 Sprays can also deposit on surfaces 

36 where contact with residues can eventually lead to indirect exposures (e.g., children playing on 

37 lawns where residues have deposited next to treated fields). The potential risk estimates from 

38 these residues can be calculated using drift modeling coupled with methods employed for 

39 residential risk assessments for turf products. There is a regulatory precedent for this approach 

40 as it has been used by the Agency in a number of previous situations that include: (1) response to 

41 a petition to cancel 14 pesticides, (2) development of buffer zone estimates for two 

42 organophosphate insecticides used on orchard crops in the Pacific Northwest, and (3) 

development of a spray drift risk assessment for an organophosphate insecticide.

5 43

44

 1 http://www.epa.gov/pesticides/science/residential-exposure-sop.html 2 http://www.epa.gov/pesticides/ppdc/2011/april/session4-ch-workerrisk.pdf and 

http://www.regulations.gov/#!docketDetail;D=EPA-HQ-OPP-2009-0889 3 This document is not intended to provide guidance for addressing mosquito adulticide and other ultra low volume 

types of applications. These analyses are completed on a case by case basis because label criteria must be accounted 

for when parameterizing the model for spray quality and other application parameters (e.g., release height).

4 Lee et al (2011) Acute Pesticide Illnesses Associated with Off-Target Pesticide Drift from Agricultural

Applications — 11 States, 1998–2006, available at the following: 

http://ehp03.niehs.nih.gov/article/info%3Adoi%2F10.1289%2Fehp.1002843

5 http://www.epa.gov/fedrgstr/EPA-PEST/2004/May/Day-26/p11779.htm and 

http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2008-0850-0105
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45 Section 2: Problem Formulation provides a brief discussion of the issues associated with spray 

46 drift and their possible implications. Section 3: Scoping outlines the criteria risk assessors 

47 should use to determine what type of assessment is needed in order to properly evaluate and 

48 characterize spray drift in risk assessment. Section 4: Method describes the techniques used to 

49 calculate risks associated with drift. Section 5: Considerations describes the factors which 

50 should be described and/or considered associated with risks from spray drift.

51

52 Section 2 Problem Formulation

53 Data summarized from 2007 indicate that about 12.4 billion dollars was spent on pesticide 

54 products domestically and that resulted in about 1.1 billion pounds of pesticides being applied 

that year.6 55 U.S. Census data from 2010 also indicate that about 90 million people live in areas 

56 classified as either rural (~30 million) or in relatively small urban clusters (~60 million) which 

57 indicates that there is a widespread opportunity for spray drift related exposures if applications

are not properly managed.7 58 

59

60 Pesticide application technology to prevent all possible spray drift is not truly feasible except 

61 under highly prescribed situations using technologies not generally available. For example, 

62 when granular formulations are applied directly into the soil no drift would be expected. 

63 Another example is that certain types of programmable controllers are used on more 

64 sophisticated application equipment to actively manage drift potential, but they are not widely 

65 used. Drift would be greatly minimized in these example situations but these types of 

66 application techniques do not work for all crop/pesticide/pest combinations. Foliar applications 

67 of sprays and other delivery techniques are prevalent in many areas of agriculture and in these 

68 situations drift is difficult to completely eliminate. There is a significant level of effort focused 

69 within the agricultural engineering community on drift reduction technologies and the 

development of best management practices.8 70 This document focuses only on evaluating spray 

71 drift in application situations that are considered compliant with label statements that prohibit 

72 application sprays from contacting people directly through drift. Situations involving direct 

73 human contact from spray drift are addressed by the Agency using other types of already existing 

74 requirements such as enforcement actions, basic requirements for worker protection, or 

75 modifying use instructions (e.g., add drift minimization language to all pertinent labels).

76

77 The EPA has developed a methodology for estimating potential risks from spray drift. This 

78 approach is based on drift modeling coupled with techniques previously designed to evaluate

79 residential turf uses of pesticides. Essentially, a residential turf assessment is conducted but the 

80 residue value inputs are adjusted to account for the amount of pesticide residue deposited as a 

81 result of spray drift instead of being based on a direct, intentional application onto turf. The 

 6 http://www.epa.gov/opp00001/pestsales/07pestsales/market_estimates2007.pdf (pgs 4 and 8) 7 http://www.census.gov/geo/reference/urban-rural-2010.html, urban clusters are defined as 2,500 and 50,000 

people, also see http://www.census.gov/population/www/censusdata/files/urpop0090.txt 8 Manufacturers of application equipment have widely integrated drift management into their product portfolios. As 

an example, refer to information at: http://www.teejet.com/english/home.aspx
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82 amount of residue which deposits from drift varies with distance from the edge of a treated field. 

83 The overall approach is illustrated in Figure 1. [Note: In Figure 1 the term “buffer” is included 

84 and the lawn area is 50 feet wide. These are explained in more detail below.]

85

86

87

88 Figure 1. Conceptual Model of Exposure Pathway Associated With Spray Drift

89

As described by various spray equipment manufacturers and the Spray Drift Task Force,9 90 spray 

91 drift levels can be directly impacted by many factors including application equipment, 

92 environmental conditions, and site characteristics. Figure 1 illustrates an aerial application but 

93 drift can occur from the use of other types of application equipment used in agriculture such as 

94 groundboom sprayers commonly used in field crops and airblast sprayers commonly used in 

95 orchards. Drift profiles differ depending upon the type of equipment used. How that equipment 

96 is configured; types of nozzles, operating pressures, ground speed, and release height among 

97 other factors can impact drift results. Environmental conditions such as wind speed, wind 

98 direction, and stability of the atmosphere can also impact the amount of sprays that drift. The 

99 higher the windspeed the more drift which occurs based on total mass of pesticide moving off100 target but changes in wind direction can lower total drift estimates in a specific area downwind 

101 because less mass is moving away from a treatment area in one direction. The characteristics of 

102 an application site also have relevance. Flat terrain in some ways can cause more drift especially 

103 if it has a low surface roughness (i.e., essentially the contour of the area that may be bare soil or 

104 field stubble) which impacts how much drift can be trapped as spray plumes move across such

105 areas.

106

107 Estimated exposures from spray drift are based on the premise that residential areas, or other 

108 public areas routinely accessible to the general population such as parks, are near where a 

109 pesticide application may occur. Exposures may occur in a variety of ways but for regulatory 

110 purposes, as noted above, this document focuses on compliant application events. In compliant 

111 application events no individual should be directly sprayed, given existing label language and 

112 requirements for worker protection, which means direct dermal and inhalation exposures to 

 9 http://www.agdrift.com/ , http://www.teejet.com/english/home.aspx
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113 sprays will not be considered. Exposures considered for risk assessment purposes occur solely 

114 as a result of contact with a surface that has been previously impacted by spray drift such as 

115 nearby lawns. There are existing methods for evaluating a variety of exposure pathways in a 

116 residential environment as described in the SOPs. Based on the SOPs it is also clear that 

117 considering the exposures of children playing on turf is an appropriate exposure scenario basis 

118 for this method given the magnitude of the resulting exposures and the relevant physical 

119 processes (see SOP 3.2). The residential turf post-application SOP provides a standard method 

120 for estimating potential dermal doses among adults and children 1 < 2 years old from dermal 

121 contact with turf that has previously been treated with pesticides. This scenario assumes that 

122 pesticide residues are transferred to the skin of adults/children who enter treated lawns for play, 

123 recreation, yardwork or other homeowner activities. Considering the strengths and limitations of 

124 available data and behavioral characteristics of potentially exposed lifestages, post-application 

125 dermal exposure is only calculated for adults and children 1 < 2 years old.

126

127 Pesticides used to treat turf are typically applied either in a broadcast type of application to 

128 ensure complete coverage across an entire lawn or they are completed using a localized approach 

129 focused only on infested areas (i.e., referred to as spot treatments). In broadcast applications, the 

130 intent is to uniformly deliver the chemical so when intentional broadcast lawn applications are 

131 evaluated in risk assessment the size of a lawn is not a key issue. This eliminates the need to 

132 address time and location factors in risk assessment. While a child could be playing anywhere on 

133 a treated lawn, the lawn would have been treated in a uniform manner and thus, exposure 

134 potential would be similar throughout any location on the treated area. When spray drift deposits 

135 onto a lawn adjacent to an application site it will also deposit across an entire lawn similar to a 

136 broadcast application with a notable exception as illustrated in Figure 1. 

137

138 When lawns are impacted by spray drift the concentration of deposited residues decreases as the 

139 distance away from a treated site increases. In order to account for this some assumptions have 

140 to be made related to how a child spends their time outdoors on a lawn. It is essentially 

141 impossible to define from a regulatory perspective a time/location approach for children

142 outdoors. Rather, the spray drift assessment uses an approach similar to that outlined in the 

143 SOPs for evaluations of indoor crack and crevice applications where residue profiles change 

144 within treated rooms (see pg 7-26/Figure 7-1/SOP 7.2.2.1). 

145

146 For spray drift risk assessment, how the amount of deposited residue changes over distance has 

147 been integrated over a turf area (e.g., lawn or public areas such as parks/playgrounds) of 

148 predefined dimensions (i.e., 50 feet wide). An average residue level over such areas is 

149 determined and it is assumed a child could be anywhere in that area while playing and being 

150 exposed to deposited residues. The dimensions of a lawn or public area where children play can 

151 impact risk estimates associated with drift because the wider the turf area where a child plays the 

152 lower residues that will be available for exposure because more dilution of deposited residues 

153 occurs with greater distance from the treated area. The characteristics of domestic housing 

154 indicate a large range of possibilities for establishing a lawn size for risk assessment purposes. 

155 The American Housing Survey completed by the U.S. Census indicates about 30.5 percent of 

156 domestic housing is multi-dwelling while the remaining are single family houses (62.7%) or 

manufactured/trailer homes (6.8%).10 157 The U.S. Census also provides information on the sizes of 

 10 http://www.census.gov/housing/ahs/files/ahs11/National2011.xls
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158 lots relative to housing type which indicates for attached one family houses the average lot size 

is 4,155 ft2 and the median is 2956 ft2 159 (2008 information presented but similar values are 

reported for years 1992-2008). For detached one family houses the average lot size is 9,070 ft2 160

and the median is 19,482 ft2.

11 161 Given this information, the lawn dimensions used as the basis of 

this methodology are 50 feet wide by 100 feet long (5,000 ft2 162 ) as illustrated in Figure 1. The 

5000ft2 163 value approximates the mean lot size for attached housing and also a reasonable 

164 representation for detached housing with smaller lots. [Note: Lot size is equated for the 

165 purposes of this discussion with lawn size and housing footprints are not accounted for in this 

166 methodology. It should also be noted that buffer zone distances are included at varying 

167 distances from adjacent to the field edge to 300 feet downwind from the field edge in this 

168 methodology.] 

169

170 Residential risk assessments are conducted based on a premise which requires that they be

171 completed for each specific scenario associated with the product in order to evaluate the potential 

172 risks associated with that use pattern. For products which allow applications to turf, for example,

173 it is assumed that homeowners and their families will be exposed on the day of application

174 through contact with treated turf. How often applications of such products occur and the 

175 persistence of resulting residues directly impact the duration of exposure. Analogous to how risk 

176 assessments are completed for turf use products, spray drift risk assessments should be 

177 completed on a similar premise which assumes impacted individuals are present in areas adjacent 

178 to agricultural fields where the pesticide of interest has been sprayed and that they have contact 

179 with that pesticide on the day of application. As with other residential assessments, the duration 

180 of exposure can be governed by many factors including pest pressure, longevity of a pesticide in 

181 the environment, seasonal use relative to the crop, costs, and issues associated with resistance 

182 management. The U.S. Census also indicates, as described above, that a large percentage of the 

183 population lives in areas where the opportunity for drift occurrences may be inherently higher 

184 than other areas of the country (i.e., ~90 million people live in rural and urban cluster settings). 

185 Given these factors it is difficult to predict how frequently exposures via spray drift may occur

186 unless such information is available concerning how a pesticide is used. As with any risk 

187 assessment process, there are potential refinements which could occur related to factors 

188 associated with use. Data that could refine the conclusions of an assessment include more 

189 information on how a particular pesticide is used including application rates, application 

190 frequency, the seasonality of its use, and the kinds of application equipment commonly 

191 employed. These factors will be considered, as appropriate, on an individual case basis.

192

193 In summary, a number of factors can impact the potential for exposure from spray drift. The 

194 remainder of this document describes how the factors have been specifically considered for the 

195 purposes of developing human health risk assessments associated with exposures from spray 

196 drift. 

197

198

199

200

201

 11 http://www.census.gov/const/C25Ann/medavgsoldlotsize_cust.xls,
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202 Section 3 Scoping 

203 This section outlines the criteria risk assessors should use to determine what type of assessment

204 is needed in order to evaluate and characterize spray drift. These criteria have been developed to 

205 assist risk assessors in first defining if there is a need for a quantitative risk assessment and 

206 second for determining what to include in a quantitative assessment if it is required. In cases 

207 where a quantitative risk assessment is not needed, a qualitative characterization piece should be 

208 developed that describes the scenarios and why a quantitative approach is not needed.

209

210 Section 3.1: Information Gathering discusses the types of information that are important to 

211 know about a pesticide and its use in order to determine if a quantitative spray drift risk 

212 assessment is needed and to guide the development of qualitative characterization. Section 3.2: 

213 Scenario Development provides guidance for risk assessors when deciding what specific types 

214 of drift calculations are needed, if a quantitative risk assessment is required.

215

216 3.1 Information Gathering

217

218 In determining if a quantitative risk assessment is needed it is important to gather the appropriate 

219 information. This includes developing an understanding of the types of end-use products that 

220 contain the pesticide and how the pesticide is used. It is also important to identify any risk 

221 assessments that have been previously completed. Proper characterization of how a pesticide is 

222 used will assist in defining which uses should be considered in an assessment and may also help 

223 eliminate some uses for further consideration (e.g., certain granular products). Having an 

224 understanding of what risk assessments have been completed is also important because the 

225 results of existing risk assessments may be useful in characterizing risks from drift or defining if 

226 additional work is required. For example, if a pesticide has existing labels for use on turf, a risk

227 assessment for that use may be considered protective of any type of exposure that would be 

228 associated with spray drift if certain criteria are met. The following list was created as a 

229 framework for reviewers to aid them in the development of the necessary information:

230

231 • What crop(s)/pest(s) are treated with the pesticide? Is there a seasonality associated with 

232 the crop(s)/pest(s) of concern? What are the application rates for each crop/pest 

233 complex? Is information available that details the typical use patterns for the pesticide?

234

235 • Is the formulation a solid or liquid? If a solid, is it applied directly or is it mixed with 

236 water or other carrier and then sprayed?

237

238 • What types of equipment are allowable and viable for the application of the pesticide?

239

240 • Are applications soil-directed or foliar? Do labels require soil incorporation? 

241
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242 • Is there an existing residential turf use? If so, has an up-to-date risk assessment utilizing 

243 the 2012 Residential Turf SOP been completed for that use? What application rate was 

244 assessed for the turf use? What were the findings of the risk assessment?

245

246 • Do product labels contain specific language related to application parameters such as 

247 specific guidance on spray quality (e.g., types of nozzles to be used or the size of droplets 

248 that are allowable)? 

249

250 • What data/information are available which may inform further refinements in a 

251 residential risk assessment that have not been included? Have these data/information 

252 been reviewed and/or otherwise summarized? Examples include: (1) whether there is an 

253 existing turf transferable residue study and whether has it been used in risk assessment, 

254 and (2) does the pesticide manifest its efficacy through systemic or contact control which 

255 can impact how the pesticide is applied – systemic compounds may be applied using 

256 larger droplets because total coverage is less of a concern?

257

258 3.2 Scenario Development

259

260 In order to define the scenarios which should be considered in a spray drift risk assessment, a 

261 categorization process was developed which provides a series of decision points for deciding if a

262 quantitative assessment is needed (Section 3.2.1) and secondly, what scenarios should be 

263 included (Section 3.2.2). In all cases there should be a qualitative characterization of the 

264 potential for spray drift based on both the information above and the screening process described 

265 below (Section 3.2.3). 

266

267 3.2.1 Needs Screening

268

269 This section describes the process that should be used to determine if a quantitative risk 

270 assessment for spray drift needs to be completed for a particular pesticide. A series of questions 

271 to consider are presented below. If the answer to any question below is “Yes” then quantitative 

risk assessment is not required.12 272

273

274 • Is the pesticide solely formulated as a granular product or in some other form that would 

275 preclude drift (e.g., rodent bait)?

276

277 • Is the pesticide solely used for direct soil injected or near soil (e.g., in-furrow)

278 applications that require immediate soil incorporation?

279

280 • Are handheld equipment or stationary devices (e.g., drip irrigation systems) the sole 

methods of application for the pesticide?13 281

282

 12A qualitative discussion of spray drift potential needs to be included in every risk assessment even if a quantitative 

analysis is not required. The questions should be used as guidance for developing such characterization pieces.

13 Note that quantitative spray drift predictions can only be made based on 3 types of agricultural spray equipment 

including groundboom sprayers, airblast sprayers, and aircraft.
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283 • Does the pesticide have an existing turf use registration? Is there an existing risk 

284 assessment for that use? Is the following condition met where the maximum application 

rate on crops adjusted by drift is less than or equal to existing turf application rates? 14 285

286

287 Appl. Ratemax crop (lb ai/A) x 0.26 ≤ Appl. Rateresidential turf (lb ai/A)

288

289 • Is there other information available, which can be documented, that indicates a 

290 quantitative assessment should not be completed? If so, such information should be 

291 provided in the risk assessment in order to document this conclusion.

292

293 3.2.2 Defining Scenarios

294

295 Deciding which scenarios need to be included in a quantitative spray drift risk assessment is 

296 highly dependent upon the details provided on the label, the pests being controlled, the timing of 

297 application, the application equipment used, and whether the pesticide acts in a systemic manner 

298 or if it works via contact. Some pesticide labels provide detailed information that describes how 

299 spray equipment should be configured for applying the specific product (e.g., the type of nozzle 

300 or spray pattern to be used). However, more often than not, no details are provided except for 

301 defining very basic criteria such as application rate, equipment types, frequency of application or 

302 how much carrier (typically water) should be used to make applications. The following 

303 approaches were developed to address each situation. 

304

305 Screening Approach: A screening approach was developed based on the use of the AgDrift 

306 model in situations where specific label guidance that defines application parameters is not 

available.

15,16 307 AgDrift is appropriate for use only when applications are made by aircraft, airblast 

308 orchard sprayers, and groundboom sprayers. These equipment types are commonplace and 

309 account for most liquid spray pesticide applications in production agriculture. When AgDrift 

310 was developed a series of screening values (i.e., Tier 1 option) were incorporated into the model 

311 and represent each equipment type and use under varied conditions. There are options for 

312 considering different spray characteristics such as fine to medium droplets for aerial applications, 

313 different sprayboom heights and spray characteristics for groundboom sprayers, and the impacts 

314 of crop canopy on orchard airblast sprayers. The screening options specifically recommended in 

315 this methodology were selected because they are plausible and represent a reasonable upper 

316 bound level of drift for common application methods in agriculture. These screening options are 

317 consistent with how spray drift is considered in a number of ecological risk assessments and in 

318 the process used to develop drinking water concentrations used for risk assessment. In all cases, 

319 each scenario is to be evaluated unless it is not plausible based on the anticipated use pattern 

320 (e.g., herbicides are not typically applied to tree canopies) or specific label prohibitions (e.g., 

321 aerial applications are not allowed).

322

 14 The value (0.26) represents the maximum fraction of the application rate that can move and deposit on lawns from 

spray drift predicted from all application methods. These lawns are in contact with the field edge and are 50 feet 

wide.

15http://www.agdrift.com/ 16 Note that for many cases the scenarios outlined in the screening approach represent actual use practice so risk 

assessors should be aware and characterize these appropriately.
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323 The screening options that are recommended include:

324

325 • Groundboom applications are based on the AgDrift option for high boom height and 

using very fine to fine spray type using the 90th 326 percentile results.

327

328 • Orchard airblast applications are based on the AgDrift option for Sparse 

329 (Young/Dormant) tree canopies.

330

331 • Aerial applications are based on the use of AgDrift Tier 1 aerial option for a fine to 

332 medium spray type and a series of other parameters which will be described in more 

333 detail below (e.g., wind vector assumed to be 10 mph in a downwind direction for entire 

application/drift event).17 334

335

336 If Application Parameters Are Available: When label directions or other information are

337 available that can be used to refine an assessment, this information should be incorporated into 

338 the risk assessment to the extent possible (e.g., specific language for a herbicide to be applied 

339 using a very coarse spray or airblast applications only on full foliage mature citrus for fruit 

340 abscission). This is a more appropriate approach than just using the screening values described 

341 above because it allows for assessments to be more reflective of actual label requirements and 

342 use practices. To this end, a series of additional scenarios were developed for this SOP. 

343 Assessors should match them to the label language as appropriate. [Note: It is anticipated that in 

344 very limited circumstances there may be label language which is not reflected in the available 

345 options. In these circumstances, additional analyses using AgDrift may be needed. If this is the 

346 case, the additional outputs that are generated will be added to the accompanying calculator and 

347 this SOP will be updated with the additional information.] The additional scenarios that are 

available, also calculated using the AgDrift model include: 18 348

349

350 • Groundboom application:

351 o High boom height coupled with fine to medium/coarse spray quality

352 o Low boom height coupled with very fine to fine spray quality

353 o Low boom height coupled with fine to medium/coarse spray quality

354

355 • Orchard airblast application:

356 o Normal canopy (Stone and Pome fruit & vineyards)

357 o Dense canopy (Citrus and tall trees)

358 o Vineyard

359

 17 AgDrift allows for consideration of even finer spray patterns characterized as very fine to fine. However, this 

spray pattern was not selected as the common screening basis since it is used less commonly for most agriculture. If 

assessors identify this use pattern it should be used as the screening criteria and deposition values associated with it 

are provided in Table 1 below. Justification for including this spray quality should be included in any assessment 

based on specific label directions for its use.

18 For groundboom and orchard airblast applications no further refinements other than the scenarios presented can be 

evaluated using AgDrift or other models at this time since the model is based on an empirical evaluation of the 

existing data and it is not a mechanistically based model. There are more options available for evaluating 

refinements for aerial applications as that model is a mechanistic model that allows for variance of a number of 

parameters (e.g., weather, plane type, nozzle numbers and location, spray quality).
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360 • Aerial applications The aerial application scenario allows for permutations based on a 

361 number of factors. A number of these have been developed and are included as possible 

362 options for assessors to consider if label language or other factors indicate that the 

363 screening level assessment is not appropriate. These include the other scenarios in 

364 AgDrift that reflect different spray quality (e.g., coarse and very coarse sprays which may 

365 be required for certain pesticides such as some herbicides) and the use of helicopters 

366 rather than fixed wing aircraft.

367

368 3.2.3 Characterization of Spray Drift Potential

369

370 The final aspect of scenario development is summarizing the information for risk managers. 

371 When quantitative spray drift risk assessments are required they should be completed as 

372 described below in Section 4. These analyses should be based on the criteria outlined above 

373 such as the form of the pesticide product(s) in question and how they are applied. The 

374 information upon which these decisions are based, including the screening criteria described 

375 above, should be described in the risk assessment. 

376

377 In many cases pesticides are marketed and/or applied in ways that preclude the need for a 

378 quantitative spray drift risk assessment but this does not eliminate the need to describe the 

379 rationale for this approach. Such descriptions should be developed for each risk assessment so 

380 impacted stakeholders can clearly understand how the approach was developed. Two examples 

381 have been compiled to illustrate this issue. 

382

383 Example 1: Formulation Type

384 When pesticides are applied directly to soil as granules with ground equipment, the drift 

385 potential is negligible so in a risk assessment context this should be described (e.g., pesticide is 

386 sold only as a granular product intended application directly to soil from ground equipment). 

387

388 Example 2: Application Equipment

389 The use of handheld equipment also can greatly reduce the potential for off-target spray drift so a 

390 quantitative evaluation of these types of scenarios is not needed. Handheld equipment reduces

391 the potential for spray drift because the spray quality is usually a coarser type which inherently 

392 minimizes drift and users also consciously control drift potential during application since they 

393 are holding the nozzle(s) in their hands and directing them during application. In summary, 

394 application methods not including groundboom sprayers, aircraft or orchard airblast sprayers do 

395 not require a quantitative assessment of spray drift. However, their use and their characteristics 

396 relative to spray drift potential should be characterized in risk assessments.

397

398

399

400
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401 Section 4 Method

402 As described above in Section 2: Problem Formulation, the approach to be used for 

403 quantitatively incorporating spray drift exposure into risk assessment is based on an assumption 

404 that applications will not result in direct exposures to individuals, since such contact would 

405 constitute a misuse. Direct exposures would include inhalation of the spray plume or being 

406 directly sprayed. Rather, the exposures addressed here would occur indirectly through contact 

407 with impacted areas, such as residential lawns, when compliant applications are conducted. 

408 Given this assumption, this methodology only presents techniques that estimate exposures for 

409 children (1 to 2 years old) and adults who have contact with turf where residues are assumed to 

410 have deposited via spray drift thus, resulting in an indirect exposure. 

411

412 The 2012 Residential SOPs prescribe a number of potential scenarios for evaluating residential 

413 exposures to pesticides. The highest potential for exposure from spray drift is from contact with 

414 outdoor areas such as lawns where drift can directly deposit. The residential turf post415 application SOP provides a standard method for estimating potential exposures to adults and 

416 children. The SOPs also indicate that small children (index lifestage of 1-2 years old) have the 

highest exposure potential when playing on “treated” turf.

19 417 The SOPs estimate dermal 

418 exposures for adults and children resulting from playing on lawns as well as oral exposures for 

419 children because they exhibit mouthing behaviors which lead to oral exposure during play. The 

420 method for calculating quantitative risk estimates associated with spray drift deposition is 

421 directly based on the existing methodology for turf pesticides with one modification to account 

422 for the amount of drift that occurs and thus impacts turf residue levels. 

423

424 Dermal exposures are based on the premise that pesticide residues are transferred to the skin of 

425 adults and children who play on impacted lawns. Similar to the evaluation of pesticides 

426 intentionally used on residential turf, it is assumed that children contact turf on the same day a

427 pesticide application is conducted and that spray drift occurs. EPA also assumes that turf does 

428 not have residues of the pesticide of concern from other sources. However, these assessments can 

429 be refined to more accurately reflect exposure over a longer period of time (e.g., a week or 

430 month) if toxicological, fate characteristics, or activity information indicate the need for such 

431 calculations.

432

433 A description of how risks from spray drift should be computed based on the SOP for turf 

434 pesticides, with the appropriate adjustment to account for the amount of spray drift, is provided 

435 below. It is based on a modification of algorithms provided in SOP 3.2.2 for estimating dermal 

436 exposure. [Note: Incorporating this modification will also automatically address spray drift for 

437 oral exposures as it is based on estimated dermal exposure – see equations 3.6 and 3.7 in SOP 

438 3.2.3.] 

439

 19 See SOPs at http://www.epa.gov/pesticides/science/USEPA-OPP-HED_Residential%20SOPs_Oct2012.pdf
U.S. EPA Office of Pesticide Programs – Residential Exposure Assessment Standard Operating Procedures, Addenda 1

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440 4.1 Current Method In Residential SOPs For Calculating Dermal Exposure

441

442 In the 2012 SOPs dermal exposure resulting from contacting previously treated turf while 

443 performing physical activities is calculated as follows (Equation 3.3 in SOPs):

444

445 E = TTR* CF1 * TC * ED

446

447 where:

448 E = exposure (mg/day)

449 TTR = turf transferable residue (μg/cm2)

450 CF1 = weight unit conversion factor (0.001 mg/μg)

451 TC = transfer coefficient (cm2/hr)

452 ED = exposure duration (hr/day)

453

454 If chemical-specific TTR data are available, the TTR on Day 0 (i.e., the day of application) 

455 should be calculated because it is assumed that individuals could be exposed to residues 

456 immediately after application. However, if data are not available, then TTR can be calculated 

457 using the following formula (Equation 3.4 in SOPs):

458

TTR= AR * F * (1-D)t 459 * CF2 * CF3

460

461 where:

TTR = turf transferable residue (μg/cm2 462 )

AR = application rate (lbs ai/ft2 463 or lb ai/acre)

464 F = fraction of ai as transferable residue following application (unitless)

465 D = fraction of residue that dissipates daily (unitless)

466 t = post-application day on for exposure is being assessed (Day 0 in this SOP)

CF2 = weight unit conversion factor (4.54 x 108 467 μg/lb)

CF3 = area unit conversion factor (1.08 x 10-3 ft2

/ cm2 or 2.47 x 10-8 acre/cm2 468 )

469

470 Dermal doses are calculated as (Equation 3.5 in SOPs):

471

472 D = E * AF / BW

473

474 where:

475

476 D = dose rate (mg/kg/day);

477 AF = absorption factor (dermal); and

478 BW = body weight (kg)

479

480
U.S. EPA Office of Pesticide Programs – Residential Exposure Assessment Standard Operating Procedures, Addenda 1

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481 4.2 Modification To SOP Method To Account For Spray Drift

482

483 The modification to SOP 3.2.2 that has been made to account for spray drift only alters Equation 

484 3.4 from the SOPs. The modified equation is presented below and it should be used to evaluate 

485 potential risks from spray drift. This equation is the same except that an additional term has been 

486 included (DF or Drift Fraction) which provides an adjustment for the amount of drift that moves 

487 into and deposits in a non-target area such as a lawn. This equation applies to situations where 

488 TTR data are not available.

489

TTR= AR * DF * F * (1-D)t 490 * CF2 * CF3

491

492 where:

TTR = turf transferable residue (μg/cm2 493 )

494 DF = drift fraction of spray drift that deposits on lawns (unitless)

AR = application rate (lbs ai/ft2 495 or lb ai/acre)

496 F = fraction of ai as transferable residue following application (unitless)

497 D = fraction of residue that dissipates daily (unitless)

498 t = post-application day on for exposure is being assessed (Day 0 in this SOP)

CF2 = weight unit conversion factor (4.54 x 108 499 μg/lb)

CF3 = area unit conversion factor (1.08 x 10-3 ft2/ cm2 or 2.47 x 10-8 acre/cm2 500 )

501

502 If chemical specific TTR data are available, the residue on Day 0 is used after it is adjusted based 

503 on the ratio of the applicable application rate for risk assessment (i.e., based on the crop of 

504 concern) and the application rate for the TTR study followed by an additional adjustment for the 

505 drift fraction factor like illustrated above.

506

507 4.3 Drift Fraction Values

508

509 Drift fraction values for different application scenarios and distances from the edge of treated 

510 fields have been developed for the scenarios described above in Section 3.2. These values were 

511 estimated using the AgDrift model as described in Attachment A of this document. They are 

512 based on the screening options described above and the alternative options that could be selected

513 if appropriate label language exists and there is adequate justification for applying the alternative 

514 options. As noted above, these values are based on the average deposition across 50 feet wide 

515 swaths of lawn (Figure 1). A range of drift fraction values are provided for lawns which are 

516 located immediately adjacent to the edge of a treated field and up to distances where the nearest 

517 edge is 300 feet from the treated field edge. For all analyses, values at the immediate field edge 

518 should be considered as the basis for risk assessment with the others providing characterization 

519 of those risks. This range of values can inform risk managers about potential management 

520 options (e.g., implementing possible buffer zones, requiring certain types of application methods 

521 to reduce risk levels to acceptable levels, or requirement of coarser spray quality compared to 

522 recommended screening scenarios).

523
U.S. EPA Office of Pesticide Programs – Residential Exposure Assessment Standard Operating Procedures, Addenda 1

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524 Drift Fractions For Aerial Applications: The spray drift deposition curves for selected aerial 

525 application scenarios, based on average deposition values at each distance of interest, are shown 

526 in Figure 2 (note that the fine to medium (F2M) curve is the recommended screening option for 

527 this SOP). The estimated drift fractions over a 50’ wide lawn for various distances downwind 

528 from the treated field are provided in Table 1. The screening level scenario recommended for 

529 risk assessment is included in the first row of the table (Fine to Medium). If label specifications 

530 exist values can be selected from other options if justified.

531

532

533 Figure 2: Aerial Deposition Curves for Various Droplet Sizes From AgDrift 

534

535 Table 1: Average Drift Fractions for a 50’ Wide Lawn Starting at Various Distances 

536 Downwind From a Field Treated Using Aerial Equipment

Droplet Size+ Distance Downwind From Treated Field (feet)

0 10 25 50 75 100 125 150 200 250 300

Fine to Medium* 0.257 0.209 0.169 0.129 0.098 0.076 0.063 0.054 0.041 0.034 0.028

Medium to Coarse* 0.211 0.156 0.115 0.082 0.058 0.044 0.035 0.029 0.021 0.016 0.013

Coarse to Very Coarse* 0.183 0.124 0.082 0.053 0.037 0.028 0.022 0.018 0.013 0.010 0.008

Very Fine to Fine* 0.373 0.340 0.305 0.262 0.226 0.197 0.175 0.155 0.127 0.108 0.095

AT401, M, 10 mph, 34% SD 0.234 0.183 0.142 0.105 0.078 0.060 0.049 0.042 0.032 0.026 0.021

WASP, M, 10 mph, 34% SD 0.218 0.171 0.129 0.086 0.063 0.049 0.040 0.034 0.026 0.021 0.018

AT401, C, 10 mph, 25% SD 0.198 0.141 0.099 0.067 0.047 0.036 0.029 0.024 0.017 0.013 0.011

WASP, C, 10 mph, 25% SD 0.171 0.121 0.084 0.053 0.038 0.028 0.023 0.018 0.013 0.010 0.009

AT401, VC, 10 mph, 20% SD 0.175 0.115 0.072 0.044 0.031 0.023 0.018 0.014 0.010 0.008 0.006

WASP, VC, 10 mph, 20% SD 0.138 0.088 0.057 0.036 0.025 0.019 0.014 0.012 0.008 0.007 0.006

*Information is based on the Tier 1 option in the AgDrift model. The fine to medium spray quality is used in this SOP as the 

basis for the screening level assessment. These are all based on fixed wing aircraft. 

+For further options the AT401 is the representative fixed wing aircraft and the Wasp is the representative helicopter. SD = 

swath displacement. SD values for non-Tier I options computed using AgDrift automated adjustment option.

Spray Quality Summaries: Fine to Medium (F2M): Dv0.5 = 255 μM; Medium (M): Dv0.5 = 294 μM; Medium to Coarse 

(M2C): Dv0.5 = 341 μM; Coarse (C) Dv0.5 = 385 μM; Coarse to Very Coarse (C2VC): Dv0.5 = 439 μM;Very Coarse (VC): 

Dv0.5 = 478 μM & Very Fine to Fine (VF2F): Dv0.5 = 137 μM – only to be used with labeling justification

537

0.000

0.050

0.100

0.150

0.200

0.250

0.300

Fraction of Applied

0 50 100 150 200 250 300

Distance Downwind From Treated Fields (feet)

AgDrift Tier 1 - Fine to Medium

AgDrift Tier 1 - Medium to Coarse

AgDrift Tier 1 - Coarse to Very Coarse

AT401, M, 10 mph, 33% SD

WASP, M, 10 mph, 33% SD

AT401, C, 10 mph, 25% SD

AT401, VC, 10 mph, 20% SD
U.S. EPA Office of Pesticide Programs – Residential Exposure Assessment Standard Operating Procedures, Addenda 1

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538 Drift Fractions For Groundboom Applications: The spray drift deposition curves for 

groundboom applications, using the 90th 539 percentile outputs and based on average deposition 

540 values at each distance of interest, are shown in Figure 3. The estimated drift fractions over a 

541 50’ wide lawn for various distances downwind from the treated field are provided in Table 2. 

542 The screening level scenario recommended for risk assessment is included in the first row of the 

543 table (High Boom/Very Fine to Fine). If label specifications exist values can be selected from 

544 other options if justified.

545

546

547 Figure 3. Deposition Curves Using Groundboom Equipment

548

549 Table 2: Average Drift Fractions for a 50’ Wide Lawn Starting at Various Distances 

550 Downwind From a Field Treated Using Ground Equipment

Boom 

Height

Droplet Size Distance Downwind From Treated Field (feet)

0 10 25 50 75 100 125 150 200 250 300

High

Very Fine to 

Fine 0.187 0.093 0.056 0.035 0.025 0.020 0.017 0.014 0.011 0.008 0.007

Low

Very Fine to 

Fine 0.085 0.032 0.020 0.013 0.010 0.008 0.007 0.006 0.005 0.004 0.003

High

Fine to 

Medium/Coarse 0.049 0.019 0.013 0.009 0.007 0.006 0.005 0.005 0.004 0.003 0.003

Low

Fine to 

Medium/Coarse 0.033 0.012 0.008 0.006 0.005 0.004 0.003 0.003 0.002 0.002 0.002

Low Boom 0.508 m (20 in), High Boom 1.27 m (50 in)

Fine to Medium/Coarse (F2M/C): Avg. Droplet size (Dv0.5) = 341 μM

551

552 Drift Fractions For Airblast Applications: The spray drift deposition curves for the orchard 

553 airblast sprayers, based on average deposition values at each distance of interest, are shown in 

554 Figure 4. The estimated drift fractions over a 50’ wide lawn for various distances downwind 

555 from the treated field are provided in Table 3. The screening level scenario which is 

556 recommended for risk assessment is included in the first row of the table (Sparse). If label 

557 specifications exist values can be selected from other options if justified.

558

0.000

0.020

0.040

0.060

0.080

0.100

0.120

0.140

0.160

0.180

0.200

Fraction of Applied

0 50 100 150 200 250 300

Distance Downwind From Treated Fields (feet)

High Boom, Very Fine to Fine

Low Boom, Very Fine to Fine

High Boom, Fine to 

Medium/Coarse
U.S. EPA Office of Pesticide Programs – Residential Exposure Assessment Standard Operating Procedures, Addenda 1

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559

560

561

562

563 Figure 4: Deposition Curves Using Orchard Blast Equipment in Various Orchard Types

564

565

566 Table 3: Average Drift Fractions for a 50’ Wide Lawn Starting at Various Distances 

567 Downwind From a Field Treated Using Orchard Blast Equipment

Crop 

Canopy

Distance Downwind From Treated Field (feet)

0 10 25 50 75 100 125 150 200 250 300

Sparse 0.1435 0.0834 0.0443 0.0200 0.0110 0.0068 0.0045 0.0032 0.0018 0.0011 0.0008

Normal 0.0030 0.0020 0.0013 0.0009 0.0006 0.0005 0.0004 0.0003 0.0003 0.0002 0.0002

Dense 0.0422 0.0279 0.0175 0.0100 0.0067 0.0049 0.0039 0.0032 0.0023 0.0018 0.0015

Vineyard 0.0080 0.0041 0.0022 0.0012 0.0008 0.0006 0.0005 0.0004 0.0003 0.0002 0.0002

Sparse (Young, Dormant): This composite orchard combines small grapefruit and dormant apple orchards.

Normal (Stone and Pome Fruit, Vineyard): This composite orchard combines grape and orchards.

Dense (Citrus, Tall Trees): This composite orchard combines almond, orange, grapefruit, small grapefruit (mist 

blower) and pecan orchards.

Vineyard: This composite curve combines grape air blast sprayer applications and may not apply to other 

application equipment. 

Note: AgDrift also contains an “Orchard” scenario which is a composite of results from all tree canopy types. Since 

it is a composite it has not been included. 

568

569

0.0000

0.0200

0.0400

0.0600

0.0800

0.1000

0.1200

0.1400

0.1600

0 50 100 150 200 250 300

Fraction of Applied

Distance Downwind From Treated Fields (feet)

Sparse Normal

Dense Vineyard
U.S. EPA Office of Pesticide Programs – Residential Exposure Assessment Standard Operating Procedures, Addenda 1

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570 Section 5 Considerations

571 There are a significant number of considerations relevant to risk characterization that should be 

572 factored into the interpretation of spray drift exposure and risk assessments completed based on 

573 this guidance. These include:

574

575 • The risk estimates calculated are based on the premise that spray drift occurs in a manner 

576 similar to that predicted and that an exposed person is at the locations and exhibits the 

577 behaviors represented in the assessment.

578

579 • The aerial drift fraction estimates are based on application to bare ground with no crop in 

580 the downwind area as well (i.e., these are referred to as a low surface roughness condition 

581 and these conditions are known to have higher drift; this is a convention in AgDrift 

582 Tier1). It should also be noted that in the drift analyses completed in the assessment, 

583 wind vectors were moving from treated areas to the downwind area of the field 100 

584 percent of the time at a constant windspeed of 10 mph which would maximize spray drift 

585 levels under the model conditions.

586

587 • Spray drift values are based on the general application of the Tier I output values from 

588 AgDRIFT and the subsequent higher tier analyses that were completed. There are 

589 uncertainties associated with all of these approaches which have been discussed 

590 extensively during the activities of the SDTF and the development of the AgDrift model. 

591 All of the associated uncertainties apply to the results of this analysis. There are 

592 additional analyses that could be completed in order to elicit how sensitive spray drift 

593 levels may be to such changes in how applications are made or the conditions during 

594 applications (e.g., evaluate impact of alternative aircraft, evaluate nozzle placement, 

595 impacts of surface roughness). 

596

597 • AgDISP (another spray drift model similar to AgDrift) could also be used if further 

598 potential refinements are needed in certain circumstances. For example, the effect that a 

599 crop canopy may have on the deposition pattern downwind of a treated field following an 

600 aerial application could be investigated. However, such an analysis would be limited 

601 because: 1) canopy simulations in AgDISP are theoretical in nature; and 2) AgDISP 

602 simulations represent uniformly closed canopy structures that are generally not expected 

603 for tree crops in an agricultural orchard setting where air movement really occurs through 

604 non-homogeneous canopies more common in agriculture. 

605

606 • The residential aspects of the calculation are based on the SOPs that have undergone an 

607 extensive review process as cited above. Associated with each calculation is a degree of 

608 uncertainty which is described in detail in the SOPs. 

609

610 • If possible, the prevalence of one application method compared to another should be 

611 considered and characterized.

612
U.S. EPA Office of Pesticide Programs – Residential Exposure Assessment Standard Operating Procedures, Addenda 1

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613 Because it can be demonstrated that spray drift occurs even if applications are compliant with 

614 labels, spray drift is being further examined as described in this SOP to quantify potential risk

615 estimates associated with exposure downwind of a treated field. There are several actions which 

616 could be taken by risk managers that would result in lower risk estimates that should be 

617 considered when incorporated into risk assessment. The impacts have been considered where 

618 feasible. These are described below as a guide for the risk assessors in developing their 

619 documents. These include:

620

621 • Reduce maximum application rates to those needed to achieve desired efficacy.

622

623 • Potentially implement buffers to alleviate potential human health risks in situations. 

624

625 • Implement drift reduction technologies and approaches consistent with possible drift 

626 reduction technologies (DRTs) that can alleviate risks including:

627

628 o require larger droplets be used to alter spray patterns and reduce drift (e.g.,

629 perhaps requiring larger nozzle sizes by specifying a droplet size distribution (i.e., 

630 Dv0.5) on the label))

631 o require larger swath displacement from field edge

632 o require lower boom release heights

633

634 • Other possible approaches, consistent with the spirit of those used recently to manage 

635 potential risks for fumigants, may also be appropriate such as: 

636

637 o drift management plans for applicators

638 o specialized training for applicators on drift management issues

639 o use of buffer credit system consistent with the concept of DRTs, supported by 

640 appropriate data

641 o place restrictions around sensitive areas such as schools

642 o encourage use of technology to manage drift such as GPS for pilots

643

644 • Restrict aerial applications based on risk findings and available mitigation options. 

645

646 Data to confirm the efficacy of any DRT measures implemented to reduce the risk estimates 

647 associated with spray drift may also be required.

648

649
U.S. EPA Office of Pesticide Programs – Residential Exposure Assessment Standard Operating Procedures, Addenda 1

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650 Attachment A: Derivation of Drift Fraction Estimates

651

652 As described in the text of this document a series of drift fraction values have been incorporated 

653 as recommended values. One scenario has been designated as the basis for a screening 

654 assessment for each type of application equipment and all others represent a potential risk 

655 assessment refinement option if the information warrants they should be considered. In order to 

656 avoid confusion, because of the nomenclature within AgDrift (e.g., Tier 1 Aerial, etc.), the same 

657 terminology has not been used as the basis of this methodology because only one Tier 1 option 

658 within AgDrift is considered as a screening estimate in this method. In other words, AgDrift 

659 Tier 1 includes both the screening level drift fractions defined in this methodology and the 

660 scenarios which may represent potential refinements (e.g., for larger droplets resulting in a 

661 coarser spray quality). For brevity, however, it is easier to describe how the drift fraction values 

662 specified in this document were calculated using the typical AgDrift Tier nomenclature even 

663 though values within a tier may represent different levels of possible refinement for managing 

664 spray drift risk concerns.

665

666 AgDrift Tier 1 Drift Fraction Values:

667 Tier I analysis for defining aerial, ground, and orchard air blast application drift fractions were 

completed using AgDRIFT20 (v2.1.1).

21 668 The AgDRIFT spray drift model is a Microsoft 

669 Windows-based computer program provided to the U.S. Environmental Protection Agency’s 

670 Office of Pesticide Programs as a product of the Cooperative Research and Development 

671 Agreement (CRADA) between EPA’s Office of Research and Development and the Spray Drift 

672 Task Force (SDTF). AgDRIFT has undergone extensive validation including evaluation by a 

FIFRA Scientific Advisory Panel. 22, 23 673

674

675 Tier I AgDRIFT is a regression model developed from SDTF data including more than 300 

676 applications made in 10 field studies covering a range of application practices for each type of 

677 application (i.e., aerial, ground, and orchard air blast applications). AgDRIFT has been formally 

678 validated by comparing its predicted outputs to 180 SDTF field trials. These data were generated 

679 for aerial applications to a distance of about 800 meters downwind of the application field edge. 

680 These field trials were conducted using pesticide (i.e., dissolved or emulsifiable) in a liquid spray 

681 and therefore they may not fully represent spray drift resulting from encapsulated or granular 

682 based pesticide formulations. If these formulations (e.g., dispersible capsules or dispersible 

683 granular) are applied using a liquid carrier and the droplet size distribution is the same as those 

684 droplet size distribution included in AgDRIFT the resulting spray drift values are assumed to be 

 20 A User’s Guide for AgDRIFT 2.1.1: A Tiered Approach for the Assessment of Spray Drift Pesticides (February 

2003). AgDRIFT V2.01 was used to model inhalation exposure concentrations.

21 AgDRIFT and AGDISP models: Models are available through Harold Thistle, US Forestry, hthistle@fs.fed.us. 22 U.S. Environmental Protection Agency. Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) Scientific 

Advisory Panel: Estimating Drinking Water Exposure as a Component of the Dietary Risk Assessment; Spray Drift 

Program, December 10-11, 1997. 23 U.S. Environmental Protection Agency. Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) Scientific 

Advisory Panel: Burholderia cepacia: Risk Assessment of a Biopesticide with Affinities to a Human Opportunistic 

Pathogen; A Consultation on Protocol Design to Assess Acute Neurotoxicity Studies following Oral Administration 

of Pesticides; Higher Tier Ecological Risk Assessment for Chlorfunapyr; Spray Drift - Review of Proposed Pesticide 

Deposition Curves to Adjacent Areas, July 20-23, 1999.
U.S. EPA Office of Pesticide Programs – Residential Exposure Assessment Standard Operating Procedures, Addenda 1

2

685 the same. Granular formulations, applied as solid materials and no liquid spray, have different 

686 drift patterns than liquid sprays, and as such need to be considered in a separate analysis. 

687 However, from a human health perspective, off-site movement of granular products would result 

688 in lower risk estimates than those for liquid products (e.g., less drift occurs and there is less 

689 exposure uptake for granules). In most cases pesticides also have liquid end-use products and an 

690 analysis for them would be protective of potential risks from granular drift.

691

692 Drift fractions are essentially a representation of the amount of drift which occurs relative to a 

693 nominal application rate (i.e., they represent how much of the target application rate is predicted 

694 to be deposited at various distances downwind of the treated field, averaged over a 50 feet wide 

695 lawn in this case). Input parameters used in the Tier I spray drift analysis are provided in Table 

696 A-1. 

697

698 Table A-1: Tier I AgDRIFT Input Parameters

Parameter Value Comments

Aerial

Equipment Air Tractor AT-401 AgDRIFT default for Tier 1

Release Height 10 ft AgDRIFT default for Tier 1

Wind Speed 10 mph AgDRIFT default for Tier 1

Surface Roughness 0.0075 m (0.3 in) Default for Tier 1 (reflects flat terrain)

Temperature Not specified AgDRIFT Tier I ground models are based on regression 

equations developed on empirical data.

Swath Displacement

0.3722 (F2M)

0.2851 (M2C)

0.2191 (C2VC)

AgDRIFT default values for Tier 1 (Users cannot alter these 

values in Tier 1, taken from User Manual in description of 

Tier I curves)

Droplet Size F2M, M2C, C2VC AgDRIFT default for Tier 1, see note re: F2M

Fine to Medium (F2M): Droplet size (Dv0.5) = 255 μM – this option is the basis for the screening value for this SOP

Medium to Coarse (M2C): Dv0.5 = 341 μM

Coarse to Very Coarse (C2VC): Dv0.5 = 439 μM

Ground1

Equipment Low Boom (LB)

High Boom (HB)

AgDRIFT default options, The high boom option is the basis 

for the screening value for this SOP

Release Height LB: 0.508 m (20 in)

HB: 1.27 m (50 in) AgDRIFT default values

Application Efficiency LB: 99.27

HB: 99.22 AgDRIFT default values

Wind Speed Not specified AgDRIFT Tier I ground models are based on regression 

equations developed on empirical data. 

Surface Roughness Not specified AgDRIFT Tier I ground models are based on regression 

equations developed on empirical data.

Temperature Not specified AgDRIFT Tier I ground models are based on regression 

equations developed on empirical data. 

Swath Width 13.72 m (45 ft) AgDRIFT default value

Droplet Size

Very fine to fine (VF2F)

Fine to medium/coarse 

(F2M/C)

Note: The VF2F option is the basis for the screening value for 

this SOP

Orchard Air Blast1

Equipment Not specified AgDRIFT orchard air blast model are based on regression 

equations developed on empirical data.

Release Height Not specified AgDRIFT orchard air blast model are based on regression 

equations developed on empirical data.
U.S. EPA Office of Pesticide Programs – Residential Exposure Assessment Standard Operating Procedures, Addenda 1

3

Parameter Value Comments

Application Efficiency

Normal: 99.85

Dense: 98.01

Sparse: 97.69

Vineyard: 99.73

Orchard: 98.63

AgDRIFT default

Wind Speed Variable AgDRIFT orchard air blast model are based on regression 

equations developed on empirical data.

Surface Roughness Not specified AgDRIFT orchard air blast model are based on regression 

equations developed on empirical data.

Temperature Variable AgDRIFT orchard air blast model are based on regression 

equations developed on empirical data.

Swath Displacement Not specified AgDRIFT orchard air blast model are based on regression 

equations developed on empirical data.

Droplet Size Not specified AgDRIFT orchard air blast model are based on regression 

equations developed on empirical data.

Orchard Type2 Normal, Dense, Sparse, 

Vineyard, and Orchard

AgDRIFT default, the sparse option is the basis for the 

screening value for this SOP

1. Regression equations were developed from SDTF field study results with groundboom and orchard blast 

equipment. The 90th percentile groundboom results are used for the purposes of this SOP. There is no higher tier 

modeling available for groundboom and orchard applications.

2. Normal (Stone and Pome Fruit, Vineyard): This composite orchard combines grape and apple orchards

Dense (Citrus, Tall Trees): This composite orchard combines almond, orange, grapefruit, small grapefruit (mist 

blower) and pecan orchards.

Sparse (Young, Dormant): This composite orchard combines small grapefruit and dormant apple orchards. 

Orchard: This composite orchard combines apple, almond, orange, grapefruit, small grapefruit, pecan, and 

dormant apple orchards.

Vineyard: This composite curve combines grape air blast sprayer applications and may not apply to other 

application equipment.

699

700 Calculation of Drift Fraction Reduction Options:

701 The concept behind the development of the DRTs and the overall guidance of the PR notice for 

702 labeling related to spray drift described above is that pesticide applicators can control drift 

703 through the use of specific equipment and application parameters. These parameters include 

704 spray nozzle size, application pressure, vehicle type and configuration, release height, 

705 formulation choice, use of additives such as surfactants, and considering terrain as well as 

706 atmospheric conditions at the time of application. Additional spray drift modeling was completed 

707 for several droplet size distributions to investigate the impact that the aircraft, wind speed, swath 

708 displacement (the horizontal offset distance between the flight line and the target area), and crop 

709 canopy have on the deposition pattern of a pesticide downwind of treated fields. These represent 

710 implementable means that applicators could potentially use to reduce drift

711

712 Tier II modeling for ground and orchard applications is not possible as AgDRIFT does not have 

713 the capability to refine the spray drift estimates for these application types; however, Tier II 

714 spray drift analysis can and was completed using AgDRIFT for aerial applications. As a Tier II 

715 assessment tool, AgDRIFT is a parameterized model that can be used to investigate specific 

716 aerial application parameters. Aerial application parameters that were investigated include: 

717 aircraft (fixed and rotary winged), different spray quality, and swath displacement (default values 

718 used but altered to correspond to change in droplet size). AgDRIFT input values for the Tier II 

719 analyses are provided in Table A-2.

720
U.S. EPA Office of Pesticide Programs – Residential Exposure Assessment Standard Operating Procedures, Addenda 1

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721 Table A-2: Tier II AgDRIFT Input Parameters

Parameter Value Comments

Aerial

Equipment Air Tractor AT-401

WASP Helicopter

One of the two default Tier II options for helicopter (rotary wing) 

applications

Release Height 10 ft AgDRIFT default value in Tier II, same as Tier 1 above

Wind Speed 10 mph AgDRIFT default value in Tier II, same as Tier 1 above

Surface 

Roughness 0.0075 m (0.3 in) AgDRIFT default value in Tier II, same as Tier 1 above

Temperature 86 °F AgDRIFT default value in Tier II, same as Tier 1 above

Swath 

Displacement

0.3351 (M)

0.2489 (C)

0.2005 (VC)

Computed values from AgDRIFT Tier II when swath width is 

adjusted using the AgDrift function in the drop size distribution 

window. All values are based on ASAE options.

Droplet Size M, C, VC See VMD values below

Nonvolatile Rate 1.49 lb/a Developed based on a typical pesticide

Spray Volume 2 gal/a Minimum required spray volume

Carrier Type Water

Medium (M): Dv0.5 = 294 μM

Coarse (C) Dv0.5 = 385 μM

Very Coarse (VC): Dv0.5 = 478 μM 

Other parameters were not changed or adjusted based on standard AgDRIFT recommendation via program prompts

except as noted for Swath Displacement adjustment and use of helicopter in Tier II.

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