spray drift modelling of wastewater effluent - gw drift modelling of wastewater effluent prepared...

Spray Drift Modelling of Wastewater Effluent

Prepared for AWT Water

Report No 1220-1-R1

July 2011

By Andrew J Hewitt, PhD

Spray Drift Modelling of Wastewater Effluent © Lincoln Ventures Ltd

Prepared for AWT Water (Report No 1220-1-R1, By Andrew J Hewitt, PhD) Page i

Document Acceptance

Action Name Signed Date

Prepared by

Andrew Hewitt

1 August, 2011

Reviewed by

Rob Connell

3 August 2011

Approved by

Kevin Hurren

3 August 2011


Prepared for AWT Water (Report No 1220-1-R1, By Andrew J Hewitt, PhD) Page ii

TABLE OF CONTENTS

Page

Executive Summary ...................................................................................................................... 1

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

2 Wairarapa Combined DistrictS ............................................................................................ 3

3 Spray Drift Task Force Studies ............................................................................................. 4

4 AGDISP Model .................................................................................................................... 6

5 Discussion ........................................................................................................................ 10

6 References ....................................................................................................................... 11

7 APPENDIX 1 – SDTF Atomisation Data Summary ................................................................ 13


Prepared for AWT Water (Report No 1220-1-R1, By Andrew J Hewitt, PhD) Page 1

EXECUTIVE SUMMARY

The off-target movement of droplets from applications of liquid sprays using chemigation/ irrigation sprinkler systems is affected by several factors such as sprinkler type (mainly through the emission droplet size spectrum), boom height, the presence/ absence of end guns and meteorological conditions particularly wind speed and direction. Assessing the exposure risk from such applications requires the use of field study data and/ or drift models with inputs such as measured droplet size spectra appropriate to typical and reasonable worst case scenarios. The present report uses both sources of information (field study and droplet size data and drift modeling) to assess the exposure risk downwind of effluent applications in New Zealand. Field drift data were cited from extensive chemigation drift studies conducted by the Spray Drift Task Force (SDTF) in the US as well as atomisation studies for a wide range of sprinkler types. The author of the present report, Dr Andrew Hewitt, was previously the Project Manager of the SDTF and also conducted many of the atomisation studies reported by the SDTF. The SDTF data are confidential to the SDTF and are included in this report for use by the Wairarapa Combined District Councils only. The SDTF data must not be reproduced or further distributed without permission from the SDTF. The studies have been peer reviewed by Scientific Advisory Panel experts in the US and accepted by the US Environmental Protection Agency for spray drift exposure risk assessment including reasonable worst-case conditions and scenarios for irrigation/ chemigation applications across the US. In addition to reference to the SDTF field study data, modeling was conducted using the AGDISP model’s ground deposition prediction algorithms initially for direct comparison with field data predictions (to validate the model use for this kind of application) and subsequently for assessing the impact of droplet size, wind speed and air temperature on spray drift relative to the Wairarapa Combined Districts. The study showed that the AGDISP ground model provides excellent predictions of spray drift deposition rates relative to the SDTF field studies. This supports the concept of the use of a combination of model predictions and field study data (for evaluating the effect of factors which cannot be modeled such as the use of end guns) for exposure risk assessment of drift from effluent applications using irrigation/ chemigation sprinkler systems. Therefore the bridge between SDTF US field data for application in the Wairarapa Combined Districts is the validated AGDISP model use for a wide range of wind speeds. The SDTF field studies showed that for high pressure (4.8 bar), high release height (3.67 m) applications, the main factor affecting drift was wind speed and not the use of end guns. For the low pressure (1.4 bar), low height (1.52 m) applications, drift was higher with the use of end guns, with wind speed being of secondary importance. There was approximately a 100-fold range of drift deposition rates at each distance downwind, depending on the sprinkler type (high or low pressure, high or low boom and coarseness of the droplet size spectrum), the presence of end guns and the wind speed. Within 25 m of the applications, deposition rates had fallen to <5% of the application rate, and by 100 m, the rates were <0.1% of the application rate. Therefore a 100m buffer zone would provide a high level of protection from drift exposure, with minimal (i.e. less than 0.1% or with some low pressure/ low height sprinkler, no end gun/ low wind speed combinations, 100 times lower than this amount) drift rates for all of the SDTF application scenarios which as noted above include reasonable worst-case conditions for the US. A level of 0.1% of the application rate could be considered to be “de minimus” drift for most applications but a complete assessment of exposure risk would require input by an expert on public health risk as to the level of exposure which constitutes a hazard (i.e. the level of concern as a fraction of the application rate). The AGDISP modelling has been used to assess spray drift exposure risk from a range of conditions (droplet size, wind speed and release height scenarios) that are typical and worst case (i.e. can be



considered to exceed ranges possible in NZ) for the Wairarapa Combined Districts in order to emphasise the impact of these variables. It showed that drift exposure can be minimised through the use of NZ best practice (i.e. normal commercial sprinkler types, low boom heights and low wind speed application conditions). The assessments are constrained by limits of the AGDISP model and available data but should encompass a near-maximum range for the intended region. The upper wind speed limit for AGDISP of 17.5 m/s (63km/hr) is close to the maximum average noted for this region and good application practice as well as common sense would preclude applications at wind speeds that high, so such a limit is more for information purposes than to suggest that spraying should occur at speeds above 12 m/s (43km/hr). The mention of specific sprinklers is for example purpose only and does not constitute an endorsement over similar technologies which may be as good or better than such examples. This report explains that buffer zones of 100 to 125 m are adequate for providing protection from drift exposure for levels of concern to 0.1% of the application rate where end guns are used. A 25 m buffer would offer protection to levels of 5% of the application rate without restrictions on end guns and other parameters, or protection to 1% of the application rate if low pressure systems and/ or wind speed limits of 4 m/s (14.4km/hr) are observed. These wind speeds are intended to include gusts if they are sustained, although the higher exposure from a very brief (i.e. non-sustained) gust would not be of concern as long as the average speed is within the recommended limits.

1 INTRODUCTION

The off-target movement and deposition of sprays applied through irrigation/ chemigation systems is affected by factors associated with the application technique, meteorological conditions, liquid physical properties and spray release position. The emission droplet size spectrum has an important role in affecting where the spray will travel. Large droplets will tend to travel rapidly toward the ground by gravity while those with diameters below approximately 100 to 200 µm may carry in crosswinds to distances downwind which are determined by factors such as their release height, wind speed and evaporation rates. The spray pressure can affect droplet size as well as velocity. Among meteorological conditions, wind speed and direction are the most important factors affecting drift. As wind speed increases, drift tends to increase while the direction determines where the deposition will occur with respect to the location of any sensitive areas. Liquid physical properties can affect atomisation as well as evaporation rates. For dilute, water-based sprays such as those in effluent applications, evaporation rates will only be of concern at relatively high temperatures where small droplets are applied. Wind speed and relative humidity can also affect evaporation rates but as most irrigation systems produce very coarse sprays, evaporation is not as important as with finer spraying systems such as those used in fogging. Spray drift exposure is usually assessed through field studies and/ or modelling. Where models have been validated for a specific application, they offer great value for relatively rapid assessment of a wide range of scenarios for application and meteorological conditions such as through sensitivity analyses. Several studies have been conducted around the world to assess the off-target drift of ground sprinkler chemigation sprays (Byers et al, 1993, 2000; Kamble et al, 1992; Kohl et al, 1985). These all agree that drift is generally not considered to be significant because there is very low spray volume within these sprays with droplet size below 300µm (Kohl and deBoer, 1984; Kohl, 1974). Most off-target movement is within a very short distance (less than 20 m) of the application. In field studies with wind speeds up to 7 m/s (25km/hr), drift levels of 10, 1, 0.1 and 0.01% of the application rate were recorded at a respective maximum distances of



15, 25, 44 and 58 m downwind (Kohl et al, 1985). In another study, Kohl measured levels below 0.01% beyond 20 m downwind. Thompson (Rhone-Poulenc, 1989) predicted drift from a chemigation system that was below 0.2% of the application rate beyond 21 m downwind. His assessments involved the use of the DREVAP model. The SDTF research was similar or higher in drift than all these other studies. The present report describes the use of the large Spray Drift Task Force drift research database and a spray drift model, AGDISP, for assessing drift exposure risk in the Wairarapa Combined Districts, New Zealand from effluent applications under various conditions of equipment and meteorology.

2 WAIRARAPA COMBINED DISTRICTS

The Wairarapa Combined Districts of NZ experiences a range of conditions that need to be considered in assessing the off-target movement of sprays including those for effluent dispersion. In the 2300 km² Masterton District, topography varies with an average altitude of approximately 110 m above sea level (http://nztopomaps.com/16562/MASTERTON). A flat location was used for the assessments in the present project. The main impact of topography is that wind speeds tend to increase with elevation however wind speed is addressed separately in the analyses discussed in the following. According to the NIWA website, meteorological conditions vary during the year and the wind speed is generally considerably lower than the maximum average of 17.5 m/s (63km/hr) applied in the assessments of the present report. It is not good practice to spray anything when the wind speed is above 12 m/s (43km/hr) because considerable displacement of the plume can occur; however for the sake of assessment of spray drift exposure risk under a range of conditions including extremes, 17.5 m/s (63km/hr) can be considered an uppermost limit (albeit excessively high by 2 times) for risk assessments. Vegetation varies but for the present assessments the surface cover is assumed to be minimal (i.e. bare ground) because that offers the highest spray drift potential. When vegetation such as grass is present, drift is readily intercepted on the foliage which in turn reduces the amount available to move off-target and hence reduces the spray drift potential. In the Wairarapa Combined Districts, effluent might be discharged using different systems. These include the following three broad categories based on relative potential risk hazard:

o Worst case - Solid set high pressure guns / large gun-hard nose / Centre Pivot end guns

o Medium case - Travelling irrigators / rotary boom irrigators o Best case - Centre pivot low pressure nozzles / linear boom irrigators / K-line.

The SDTF studies with high pressure systems and end guns cover the worst-case scenarios above. The following sections of this report address the spray drift exposure risk from worst case (e.g. end guns, high booms, high pressure systems, wind speeds 7.5 – 12 m/s (27 – 43km/hr) and evaluated in this report up to 17.5 m/s (63km/hr)) through to medium case (applications

http://nztopomaps.com/16562/MASTERTON



without end guns, wind speeds 5 – 7.5 m/s (18 – 27km/hr)) to best case (no end guns, low pressure/ low boom applications or applications with wind speed <5 m/s with higher risk scenarios) systems for the range of conditions occurring in the Wairarapa Combined Districts.

3 SPRAY DRIFT TASK FORCE STUDIES

The only chemigation/ irrigation drift studies which have been conducted according to Good Laboratory Practice Standards (GLPS) and accepted for regulatory use in the US following thorough peer and scientific advisory panel review were those of the Spray Drift Task Force (SDTF) (Hewitt, 1995, Johnson, 1995). The author of the present report served as Project Manager of the SDTF and authored or co-authored several of these reports as well as the associated AgDRIFT model based on the AGDISP model. Although the SDTF studies involved chemicals rather than effluent, the SDTF research clearly showed that drift is generic in that droplets drift based on physical processes (droplet size, release height, wind speed, etc) rather than on the content of the droplets (e.g. chemical or effluent). The impact of a given amount of drift is product-specific, depending on factors such as toxicity and sensitivity. Hence the present report addresses the exposure risk which is generic and equally viable for chemicals or effluent from the SDTF studies and subsequent AGDISP modelling. The SDTF data are discussed here under permission for review by the Wairarapa Combined District Councils and are not available for other groups or users without permission, for example for use by chemical companies. The SDTF data are used here to validate the AGDISP ground model for use in predicting drift from chemigation/ irrigation applications because previous validation work with AGDISP has only been for agricultural and forestry application scenarios. Secondly, the SDTF data are discussed in view of their encompassing application scenarios which cannot be assessed using AGDISP such as the use of end guns. The SDTF was formed in the late 1980’s in response to a data call-in from the US Environmental Protection Agency (US EPA) on spray drift for chemical applications from aircraft, ground boom sprayers, orchard airblast sprayers and irrigation/ chemigation sprinkler systems. US EPA required data to be collected according to GLPS under conditions encompassing reasonable worst case scenarios for spray drift exposure risk. The SDTF conducted hundreds of field studies and extensive associated wind tunnel atomisation studies to develop its database on drift from these application platforms. The research budget of the SDTF was $23M US dollars and the studies involved hundreds of scientists from around the world. The data are protected under data compensation laws in the US aimed primarily at assuring that any chemical companies who need to submit spray drift data to US EPA contribute financially toward the work, and permission for the use of the data by the author of the current report has been granted for specific use only by the Wairarapa Combined District Councils in assessing spray drift exposure risk from effluent applications in NZ. The SDTF chemigation studies were conducted in central Washington state near Moses Lake. A centre-pivot sprinkler irrigation system was used with and without end guns in drift studies under various meteorological conditions. High pressure (4.8 bar) impact sprinklers were tested on rigs with relatively high release position (3.66 m above ground), emitting 0.09 inches of spray per acre. In comparison, low pressure (1.4 bar) Nelson S-30 spinners were tested on relatively low booms (1.52 m above ground), emitting 2.5mm/A of spray. Tests were conducted with and without end guns. Additional tests were conducted for the configurations without end guns with the wind blowing from the edge of the irrigated radius



toward the central pivot for comparison with the standard applications with the wind blowing away from the central pivot. The end wheel circumference was 1072 m. The distance from the pivot to the end wheel was 171 m, with the distance to the end sprinkler being 175 m and the distance to the end gun (if present) 177 m. The wetting radius of the end sprinkler/ end gun was 8, 15 or 23 m depending on the scenario (i.e. 8 m for the low pressure spinner, low boom, no end gun scenarios; 15 m for the high pressure impact sprinkler, high boom, no end gun scenarios and 23 m for the applications with end guns). The irrigated areas were of radius 181 (no end guns) to 200 m (end guns), representing treated areas of 2.6 to 3.1 ha. The time required to treat one quarter of an irrigated circle was 90 minutes. Spray drift was measured using horizontal alpha cellulose cards (similar to blotting paper which has a high collection efficiency for spray drift, with a 1000 cm2 surface area per card) placed on the ground at 9 distances between 8 and 305 m downwind of the application. Air samplers and vertical alpha cellulose cards were also used but the main data of interest in the studies were those from the deposition cards because drift is only usually an exposure concern once the particles deposit in an off-target area. Chemical tracers were included in the tank mix which allowed off-target drift to be assessed as a percent or fraction of the application rate. This allows the data to be generically applied for assessing the exposure risk from any chemical or applied product as a proportion of the application rate to a field. Risk assessors then routinely use such data to set appropriate no-spray buffers at the distance beyond which deposition is lower than the level of concern for the product being assessed. For example, while some miniscule amount of any material released into the atmosphere will potentially travel very large distances, most chemicals are only an exposure concern at levels well above 1% of the application rate. If the hypothetical level of concern was 1% for a given product, then it’s associated buffer zone could be set based on the distance at which distance is below 1% (or fraction of 0.01) of the application rate. In the SDTF field studies, all measurements were replicated with three sets of collectors, with excellent agreement between the replicate samples. The SDTF field studies were accompanied by atomisation studies to measure the emission droplet size spectra from a wide range of sprinkler types and use conditions (e.g. spray pressure). The sprinkler and nozzle types selected for the research were based on surveys of thousands of applicators/ farmers/ growers across the US, and we consider them applicable to common practice in NZ. These included the following types: floodjet and solid stream nozzles, Nelson S30 and R300 spinners, Senninger 360 Superspray, Senninger Wobbler, Nelson F44AAB and F33AS impact sprinklers and Senninger Quad Spray and LDN sprinklers. These produced a wide range of droplet size spectra with volume median diameter (Dv0.5) droplet size values between 500 and >5000µm and fine droplet components (droplets with diameter below 100µm) of 0.01 to 2%. The volume median diameter is the droplet diameter at which half of the spray volume is contained in smaller droplets. The larger its value, and the smaller the spray volume in droplets with diameter below 100µm, the lower the general drift potential of the spray if all other variables are equal. Therefore the reasonable worst-case drift exposure would be expected to be for the finest sprays. The SDTF atomisation data are summarised in Appendix 1. Figure 1 summarises the main SDTF chemigation data for 6 application scenarios showing a 10-100 fold range in deposition rates at each distance downwind of the application.



Figure 1. Off-Target Deposition Rates for Chemigation Treatments in SDTF Field Studies

Downwind deposition for the high pressure treatments showed a direct correlation with wind speed, irrespective of whether or not an end gun was used. For the low pressure treatments, greater downwind deposition was measured when an end gun was used than with no end gun. Wind speed was of secondary importance with the low pressure treatments. For the treatments with the wind blowing towards the pivot (rather than away from it), the high pressure treatment resulted in greater drift than the low pressure treatment. The SDTF studies including all of the application platforms (not only the chemigation ones, but the aerial, ground and orchard studies) showed that among meteorological factors, wind speed and direction are the variables of concern for spray drift with temperature and relative humidity being of relatively low importance.

4 AGDISP MODEL

AGDISP is a model which was developed by the US Forest Service and its co-operators for modelling the dispersion, transport and deposition of sprays applied from various platforms. The model includes aerial and ground application systems. Of interest in the present project was the ground model. The parameters from one of the SDTF field study application scenarios (Treatment 4-1) were entered into the AGDISP ground model, including wind tunnel atomisation data for the sprinkler type, the Nelson S-30. Treatment 4-1 involved the use of this low pressure (1.4 bar) sprinkler on a 1.52 m high boom with an air temperature of 22°C, relative humidity of 28% and wind speed 3.7 m/s (13.3km/hr). The field deposition data and model-predicted deposition curve are shown on Figure 2. This was selected as a representative treatment for the Wairarapa Combined Districts conditions and the agreement between the model and field data is excellent with a slight over-prediction beyond 30 m which is environmentally-conservative.

0.0001

0.001

0.01

0.1

1

10

100

0 50 100 150 200 250 300 350

De

po

siti

on

(p

erc

en

t o

f ap

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n r

ate

)

Downwind Distance (m)

4.8bar, 3.7m, end gun, 4.2 m/s


4.8bar, 3.7m, 1.1 m/s

4.8bar, 3.7m, 5 m/s



1.4bar, 1.5m, 4.1 m/s

1.4bar, 1.5m, 1.4 m/s

4.8bar, 3.7m, 1.9 m/s toward pivot






Figure 2. Model-Predicted and Field-Measured Deposition for Chemigation Application 4-1

Figure 3 shows the effect of wind speed within the limits allowed by AGDISP (up to 17.5 m/s (63km/hr)), which is close to the maximum average in Wairarapa Combined Districts, upon spray drift. This is for modelling the reasonable worst-case scenario of a relatively fine spray (Dv0.5 = 500 µm) with relatively high boom (3.7 m) but without an end gun because the model cannot practically cover end gun usage (hence the field study data are optimal for such applications). The following table summarises the buffer zones that would correspond to each wind speed for this reasonable worst-case assessment for exposure levels of 1% and 0.5% of the application rate, with all of the calculated buffers falling within the proposed 120m limit.

Wind speed Buffer for 1% of Application Rate Buffer for 0.5% of Application Rate

20 km/h 25 m 35 m

35 km/h 35 m 75 m

45 km/h 50 m 100 m

55 km/h 60 m 110 m

65 km/h 75 m 120 m

0

0.05

0.1

0.15

0.2

0.25

0.3

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0 50 100 150 200 250 300 350

De

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(fr

acti

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of

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rat

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Downwind Distance (m)

Field 4-1

Model 4-1



Figure 3. AGDISP-Predicted Deposition for Reasonable Worst-Case Chemigation Application at Different Wind Speed Conditions

The off-target drift increased with higher wind speed, which is consistent with field study findings, but with deposition rates remaining below 0.005 (0.5%) of the application rate by 100 m downwind even at the highest modelled wind speed of 17.5 m/s (63km/hr). Figure 4 shows that wind speed was more important than temperature in affecting drift with higher wind speeds causing an increase in drift and higher temperatures causing a slight increase in drift. These modelling runs were all conducted at a reasonable worst-case condition of very low relative humidity (i.e. favourable conditions for evaporation which increases drift potential).



Figure 4. AGDISP-Predicted Deposition for Reasonable Worst-Case Chemigation Application at Different Temperature and Wind Speed Conditions

Figure 5 shows the impact of droplet size (sprinkler type) on spray drift. As droplet size increases, the deposition rates at each distance downwind decrease but are still below 0.01 (1%) at 100 m downwind even for the finest spray. It should be noted that most of the chemigation sprinklers tested in the SDTF atomisation studies produced sprays with Dv0.5 values in excess of 2500 µm which would produce de minimus drift as shown on this graph. The only sprinklers which produced finer sprays than 2500 µm in the SDTF atomisation studies were as follows: Nelson F33AS at high pressure (5.5 bar); Nelson F44AAB at high pressure (4 bar) (these sprinklers produce coarser sprays than 2500 µm at pressures ≥1 bar below these levels); Senninger 360° ss at all pressures; Senninger Wobbler at pressures above 1.4 bar; Senninger Quad at all pressures; Senninger LDN at all pressures; and Nelson S30 at all pressures.



Figure 5. AGDISP-Predicted Deposition for 1.52 m Boom Height Chemigation Applications With Different Dv0.5 Droplet Size Values

5 DISCUSSION

The SDTF field studies show that field testing of chemigation/ irrigation sprinklers under typical and reasonable worst-case conditions provides drift which decreases rapidly with distance downwind of the application. Beyond approximately 180 m, drift levels are nominally insignificant and at fairly flat levels (i.e. there is no significant further decrease in deposition rates beyond ~180 m). A wide range of deposition rates occurs depending on the sprinkler type and height; the use or absence of end guns and the ambient wind speed. The highest level of drift measured in the SDTF field studies at a distance of 100 m downwind of the application is 0.1% of the application rate, with that scenario involving the high pressure, high boom, relatively fine spray emitted into a relatively high 4.2 m/s (15.1km/hr) wind. The same application at half the wind speed produced a deposition rate at 100 m of 0.02% applied. The highest deposition rate at 100 m for applications without end guns was similar to the 0.1% deposition rate, when the wind speed was high (5 m/s or 18km/hr), but ten times lower (0.01%) in a 1.1 m/s (4km/hr) wind speed. Low pressure, low boom applications produced very low drift with values being below 0.04% with an end gun and below 0.009% without an end gun. When compared to other chemigation field studies, the SDTF research tends to be “worst case” (higher drift rates) because the studies were designed for regulatory use which involved worst-case scenarios. The report has addressed high, medium and low drift exposure risk scenarios applicable to Masterton with the high risk scenarios being applications with end guns on high booms in wind speeds above 7.5 m/s (27km/hr); the



medium risk scenarios including travelling irrigator type of spray gun on low booms with wind speeds above 5 m/s (18km/hr) and the low risk scenarios being applications without end guns using low pressure systems, or applications with other systems where the wind speed is below 5 m/s (18km/hr). Low booms (~1.5 m) and coarser sprays associated with low pressure systems (Dv0.5 ≥1500 µm) are conducive to lower drift levels. When considered in conjunction with the field data, the modelling runs support the following recommendations for chemigation applications in the Masterton area for minimising off-target drift to de minimus levels (with options for deposition rates below 0.1 and 0.01 of the application rate):

Observe a buffer zone distance of at least 100 m to 125 m to keep deposition rates below 0.1% of the application rate

Buffer zones of 25 m will afford protection to 5% of the application rate without restrictions on end guns and other parameters, or protection to 1% of the application rate if low pressure systems and/ or wind speed limits (including sustained gusts) of 4 m/s (14.4km/hr) apply. If a level of protection to 0.1% is required with a 25 m buffer, then end guns and high pressure/ high boom systems must not be used. In other words, for <0.1% deposition rates with a 25 m buffer, low pressure (≤1.4 bar), low boom (≤1.52 m) sprinkler systems without end guns are required.

6 REFERENCES

Byers, M.E., Kamble, S.T. and Witkowski, J.F. (1993) Drift During Center-Pivot Chemigation of Chlorpyrifos with and without Crop Oil. Bull. Environ. Contam. Toxicol. 51, 60-7. Byers, M.E., Kamble, S.T. and Witkowski, J.F. (2000) Assessing Insecticide Drift During and After Center-Pivot Chemigation to Corn Using Glass Plates and Gauze Pads. Bull. Environ. Contam. Toxicol. 65, 522-9. Hewitt, A.J. (1995) Spray Drift Task Force Atomisation Droplet Size Spectra of Sprinklers Used in Chemigation. SDTF Report No. A93-007, MRID No.43845501. Johnson, D. (1995) Spray Drift Task Force 1994 Field Chemigation Study. Report F94-022. Kamble, S.T., Byers, M.E., Witowski, J.F., Ogg, C.L. and Echtenkamp, G.E. (1992) Field Worker Exposure to Selected Insecticides Applied to Corn via Center-Pivot Irrigation. J. Econ. Entomol. 85, 974-80. Kohl, R.A. (1974) Drop Size Distribution from Medium-Sized Agricultural Sprinklers. TRANS ASAE 17, 690-3. Kohl, R. A. (1985) Chemigation Drift Potential. ASAE Paper 85-2576, Chicago, Illinois. Kohl, R.A. and DeBoer, D.W. (1984) Drop Size Distribution for a Low Pressure Spray Type Agricultural Sprinkler. TRANS ASAE 27, 1836-40. Kohl, R.A., Kohl, K.D. and DeBoer, D.W. (1987) Chemigation Drift and Volatalization Potential. Applied Eng. In Agriculture 3, 174-7.



McDonald, Dines, Couper (AWT NZ Ltd) (2010), Masterton Wastewater Land Application Scheme – Preliminary Report for Discussion. 68 pp. Rhone-Poulenc Ag Company (1989) Wind drift and evaporation potential of chemical application of MOCAP EC in center pivot irrigation systems. EPA correspondence No. 89-341 sent to EPA on October 6 regarding Ethoprop Registration Standard. (EPA Reg. No. 264-458).



7 APPENDIX 1 – SDTF ATOMISATION DATA SUMMARY

The following table summarises the mean atomisation data from the SDTF studies. Many sprinklers comprised multiple jets which were sampled individually and used to determine flow-weighted mean size spectra by weighting each jet contribution to the total relative to its proportional mass. The droplet size data have been rounded in this table for ease of reading and comparison. All data are based on three replicate measurements.



Sprinkler

Type

Sprinkler

Setting

Pressure

(psi)

Flowrate

(L/min)

Dv0.5

(µm)

Vol<100µm

(%)

Vol<136µm

(%)

Nel. S30 D4 8° 9/64 5 3.8 4000 0.01 0.02

Nel. S30 D4 8° 9/64 10 5.7 3900 0.03 0.08

Nel. S30 D4 8° 9/64 20 9.1 3500 0.28 0.85

Nel. S30 D4 8° 7/32 5 10.6 5200 0.06 0.14

Nel. S30 D4 8° 7/32 10 15.1 5400 0.11 0.29

Nel. S30 D4 8° 7/32 20 22.3 5000 0.16 0.41

Nel. R300 D4 8° 9/64 15 7.6 3500 0.05 0.20

Nel. R300 D4 8° 9/64 30 10.6 4100 0.14 0.42

Nel. R300 D4 8° 9/64 50 14.5 4000 0.16 0.53

Nel. R300 D4 8° 7/32 15 18.9 4600 0.01 0.06

Nel. R300 D4 8° 7/32 30 28.0 3100 0.09 0.33

Nel. R300 D4 8° 7/32 50 36.0 3900 0.18 0.58

Nel. F44AAB 9/64 20 9.64 4200 0.02 0.10

Nel. F44AAB 9/64 40 13.58 2700 0.04 0.22

Nel. F44AAB 9/64 60 16.85 1900 0.08 0.48

Nel. F44AAB 7/32 20 21.95 5500 0.01 0.05

Nel. F44AAB 7/32 40 29.27 3600 0.03 0.15

Nel. F44AAB 7/32 60 36.7 2600 0.06 0.31

Nel. F33AS 9/64 20 9.5 4400 0.03 0.12

Nel. F33AS 9/64 40 13.5 2800 0.04 0.19

Nel. F33AS 9/64 80 18.2 1700 0.10 0.55

Nel. F33AS 7/32 20 22.61 5400 0.03 0.11

Nel. F33AS 7/32 40 30.2 4100 0.05 0.19

Nel. F33AS 7/32 80 44.92 3000 0.08 0.33

Sen. 360°ss CM1 8/64 20 6.8 440 1.4 4.8

Sen. 360°ss CM2 8/64 20 6.81 1000 0.4 1.3

Sen. Wobbler 9/64 10 5.7 3200 0.1 0.4

Sen. Wobbler 9/64 20 8.7 1100 1.0 3.0

Sen. Wobbler 9/64 40 12.9 1100 1.3 3.7

Sen. Wobbler 16/64 10 20.4 7700 0.2 0.2

Sen. Wobbler 16/64 20 29.5 4100 0.4 0.4

Sen. Wobbler 16/64 40 42.0 1100 0.0 0.0

Sen. Quad CM1 10/64 6 5.3 1600 0.02 0.09

Sen. Quad CM2 10/64 6 5.3 1000 0.4 1.5

Sen. Quad CM1 16/64 10 19.8 2600 0.05 0.2

Sen. Quad CM2 16/64 10 20.1 1200 0.5 1.7

Sen. LDN CM1 16/64 6 16.3 1900 0.01 0.03

Sen. LDN CM1 16/64 15 26.1 2000 0.01 0.04

Sen. LDN CM1 20/64 6 25.4 1600 0.27 1.0

Sen. LDN CM1 20/64 15 40.9 1100 0.59 2.1

TK3 Deflector 10 1.1 900 0.35 0.86

Nel. S30 Red 9/64 20 8.7 1000 0.7 2.3

Nel. S30 Red 7/32 20 23.1 1700 0.4 1.3

Nel. F44AAB 17/64 20 30.59 5700 0.01 0.03

Nel. F44AAB 17/64 40 45.6 3800 0.02 0.08

Nel. F44AAB 17/64 60 53.7 3900 0.02 0.09

Nel. F33AS 7/64 70 10.5 1600 0.01 0.08

Nel. F33AS 7/64 80 11.9 1500 0.02 0.26

Spray gun D6 100-160 5.6-9.1 180-490 3-12 10-40

Nel. S30 D6-12 9/64 20 6.0 420 1.5 4.7

spray drift modelling of wastewater effluent - gw drift modelling of wastewater effluent prepared...

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