development of a surface water exposure module for the ... of herbicide loads during run-off or...

J.M. Hollis. Specialist, Pesticide Environmental Fate. 58, St. Annes Rd., London Colney, St.Albans, Herts. AL2 1LJ, UK

Tel: 01727 823810 E-mail: [email protected]

Development of a Surface Water Exposure Module

for the HardSPEC Railway Scenario

by

J.M. Hollis

May 2010

Report for the Hard Surfaces Steering Committee

1

Foreword

Opinions expressed within this note are those of the author and do not necessarily reflect the

opinions of the sponsoring organisation. No comment within this report should be taken as an

endorsement or criticism of any herbicide compound or product.

Reference to this report should be made as follows:

HOLLIS, J.M. (2010). Development of a Surface Water Exposure Module for the HardSPEC

Railway Scenario. Report for the Hard Surfaces steering committee. 38 pp plus 1 Appendix

Development of a Surface Water Exposure Module for the HardSPEC Railway Scenario. May 2010

2

SUMMARY

The HardSPEC model v 1.2.1 is recommended by the UK Chemicals Regulations Directorate for use

in calculating first-tier Predicted Environmental Concentrations (PEC‟s) in surface and groundwater

resulting from a proposed use of herbicides on hard surface environments. However, no methods for

calculating PEC‟s in surface water bodies associated with railways are incorporated into this model

and this has been identified as a significant limitation with respect to regulatory concerns relating to

herbicides where the proposed non-agricultural use is limited to railway networks.

This report describes the development and characteristics of a new module within HardSPEC that can

be used to calculate Surface Water PEC‟s in a small ditch adjacent to the double railway track similar

to that used in the HardSPEC Groundwater scenario. The module addresses exposure resulting from

spray drift, run-off and leaching through the railway ballast formation.

An identified realistic worst-case surface water body is the relatively static, small 1 metre wide ditch

defined for the FOCUS surface water scenarios (Linders et al, 2003). Such a surface water body is

only likely to be present in low-lying situations where it is hydro-dynamically connected to a shallow

groundwater body and water movement in the ditch is primarily groundwater flow. In such situations,

any railways present are carried on embankments and such ditches thus usually lie alongside that

embankment. The methodologies developed to characterise this situation cover losses from spray

drift (based on measured data), both as a result of application from a „spray train‟ mounted with the

„Radiarc‟ nozzle system (now used as a matter of routine by „Network Rail‟), and as an ad hoc

localised application from a hand-held sprayer along the edge of the track. They also cover losses

from any leaching and run-off that may occur following percolation of the applied herbicide through

the railway formation. The module that has been developed incorporates the following realistic

worst-case characteristics related to various components of the scenario.

Significant rainfall (5mm) occurs on the day after application.

A 75th percentile wettest spring rainfall sequence follows application.

There is a maximum spray target area for leaching and run-off simulation because both „up‟ and

„down‟ sets of tracks are sprayed.

There is a large spray target area for local hand-held application: A 1m wide swath.

As a first tier assessment it is assumed that herbicide is applied to 100% of the target area.

Drift from the spray train is based on the worst-case wind direction which is in the same direction

as that of the sideways pointing nozzles nearest to the ditch.

The amount of drift from the spray train is based on experimental data and an absolute worst-case

wind speed of 12 miles hr-1

derived from recommendations in the code of practice for using plant

protection products (Defra, 2006).


3

The 90th percentile largest losses for most ground applied sprays (2.8 %) from the FOCUS_SW

EU drift calculator are used to calculate spray drift from local hand-held applications (and from

„down track‟ drift losses from the spray train).

88% of the loads leaching out of the railway formation contribute to run-off to surface water.

As a first tier assessment it is assumed that there is no attenuation of herbicide loads during run-

off to the surface water body.

There is no attenuation of loads leached out the railway formation during transport in the

unsaturated zone.

Transport in the saturated zone only considers attenuation from partitioning and longitudinal

dispersion.

The surface water body is a small 1m wide ditch directly next to the railway embankment and with

characteristics similar to those of the FOCUSsw ditch.

Fate dynamics in the ditch are similar to those used in the „STEPS1-2 in FOCUS‟ exposure

assessment, except that all of the previous day‟s residual aqueous phase mass is lost through

groundwater flow out of the ditch because the water body is not static.

The developed railway surface water exposure module has been incorporated into a modified version

of the HardSPEC model, version 1.3.4.

Absolute worst case assumptions of 100% of the track target area receiving spray application and no

attenuation of herbicide loads during run-off or unsaturated zone leaching are included as default

input parameters. Simulations based on such parameters should be considered as first-tier

exposure assessments. However, the parameters can be changed by users to less extreme values,

providing such a change is based on a justified argument. Such modified simulations can be

considered as second tier exposure assessments as they incorporate more realistic assumptions for

these two default parameters but retain the remaining identified worst-case characteristics of the

rainfall patterns, railway track formation, its embankment and associated water body.

Simulated daily PECsw in the Railway ditch for six „test compounds‟ showed that, with the exception

of weakly sorbed compounds such as atrazine and diuron, peak daily aqueous phase PECs in the

railway ditch are the result of spray drift on the day of application. This contrasts with the HardSPEC

stream scenarios where only the most strongly sorbed compounds oxadiazon and glyphosate have

peak daily aqueous phase concentrations resulting from spray drift.

For the most mobile compounds, atrazine and diuron, exposure patterns in the railway ditch are very

different for the leaching and run-off situations and in general, from the day after application, run-off

gives slightly higher concentration peaks than leaching. However, such differences decrease

significantly with increasing compound sorption and, for the least mobile compounds, oxadiazon and


4

glyphosate, leaching and run-off inputs are so small that daily aqueous phase concentrations depend

almost entirely on residual masses from spray drift inputs on the day of application.

Comparison of model predictions with measured data is difficult because of the limited amount of

measured data available and significant differences in the dynamics of the water bodies simulated by

the model and sampled in the field study. . Nevertheless, the limited comparisons possible indicate

that when the railway scenario is adapted to match the application conditions of the field study, the

predicted peak concentrations leaching out of the railway ballast are similar to those measured in the

water sampled from ballast trenches in the field study. When the model results are modified to match

the timing of the measured peak and integrated using 3 day running average values to try to better

reflect the study conditions, they show a very similar pattern in concentrations to that measured,

although concentrations after about 42 mm accumulated rainfall appear to be under-predicted.


5

Contents

FOREWORD ........................................................................................................................................................ 1

SUMMARY ........................................................................................................................................................... 2

1 INTRODUCTION ........................................................................................................................................ 6

2 METHODS FOR CALCULATING PECSW RESULTING FROM SPRAY DRIFT, RUN-OFF AND

LEACHING FOLLOWING HERBICIDE APPLICATION TO A RAILWAY .................................... 7

2.1 IDENTIFICATION OF THE SURFACE WATER BODY ........................................................................................ 7 2.2 SPRAY DRIFT ............................................................................................................................................. 9

2.2.1 Application from a ‘spray train’ mounted with the ‘Radiarc’ nozzle system. .................................. 9 2.2.2 Localised application by a hand-held sprayer along the edge of the railway track nearest to the

surface water body. ........................................................................................................................ 17 2.2.3 Fate in the surface water body ....................................................................................................... 18

2.3 RUN-OFF .................................................................................................................................................. 18 2.3.1 Run-off simulation .......................................................................................................................... 19 2.3.2 Fate in the surface water body ....................................................................................................... 20

2.4 LEACHING ............................................................................................................................................... 21 2.4.1 Herbicide application, interception by plants and spray drift ....................................................... 21 2.4.2 Leaching through the railway formation ....................................................................................... 22 2.4.3 Transport through the railway embankment .................................................................................. 22 2.4.4 Transport in the saturated zone ..................................................................................................... 22 2.4.5 Calculation of total loadings flowing into the ditch ....................................................................... 23 2.4.6 Fate in the surface water body ....................................................................................................... 23

2.5 SUMMARY OF „WORST-CASE‟ ASSUMPTIONS IN THE METHODOLOGY ....................................................... 24 2.5.1 Rainfall patterns ............................................................................................................................. 24 2.5.2 Herbicide application .................................................................................................................... 24 2.5.3 Spray drift ...................................................................................................................................... 24 2.5.4 Run-off ........................................................................................................................................... 24 2.5.5 Leaching ......................................................................................................................................... 24 2.5.6 Fate in the surface water body ....................................................................................................... 24

3 ADAPTION OF THE HARDSPEC MODEL (V. 1.2.1) TO INCORPORATE THE NEWLY

DEVELOPED RAILWAY SURFACE WATER EXPOSURE MODULE. .......................................... 25

3.1 WORKSHEET “HERB_PROPS”................................................................................................................... 25 3.2 WORKSHEET “OUTPUT” ........................................................................................................................ 26 3.3 WORKSHEET “RAILWAY_SCENARIO” ...................................................................................................... 27 3.4 WORKSHEET “LOSSES_BR” .................................................................................................................... 27 3.5 NEW WORKSHEET “RAILWAY_SURFACE_WATER” .................................................................................. 27 3.6 WORKSHEET “LOSSES_AR” .................................................................................................................... 28

4 EVALUATION OF RESULTS FROM THE NEW RAILWAY SURFACE WATER MODULE ...... 29

4.1 COMPARISON OF PECSW SIMULATIONS USING THE NEW RAILWAY MODULE WITH OTHER HARDSPEC

SURFACE WATER MODULES ...................................................................................................................... 29 4.2 COMPARISON OF THE SURFACE WATER MODULE RESULTS WITH MEASURED DATA .................................. 30

5 CONCLUSIONS ......................................................................................................................................... 38

6 REFERENCES ........................................................................................................................................... 40

APPENDIX 1....................................................................................................................................................... 41


6

1 INTRODUCTION

The HardSPEC model (Hollis et al, 2004) is now recommended by the UK Chemicals Regulations

Directorate for use in calculating first-tier Predicted Environmental Concentrations (PEC‟s) in

surface and groundwater resulting from a proposed use of herbicides on hard surface environments.

The model produces relevant aquatic PEC‟s for four exposure scenarios:

1. A surface water stream receiving surface drainage from a major road in a rural setting where the

hard surface areas drain via gully pots. The stream also receives drainage from an adjacent 1ha

agricultural field.

2. A surface water stream receiving surface drainage from an urban catchment within which the hard

surface areas drain via gully pots.

3. A pond receiving surface drainage waters from an urban catchment within which the hard surface

areas drain via gully pots. This scenario is intended to be similar to the use of collecting ponds

within Sustainable Urban Drainage Systems (SUDS).

4. The abstraction point of a local groundwater body that receives herbicide leached from a double

railway track which crosses the groundwater catchment.

The model thus does not include any scenario that is used to calculate PEC‟s in a surface water body

receiving drainage from a railway track to which herbicides may be applied. The Hard Surfaces

Steering Committee has identified this as a significant limitation of the model with respect to

regulatory concerns relating to herbicides where the proposed non-agricultural use is limited to

railway networks.

This report describes the development and characteristics of a new module within HardSPEC that can

be used to calculate Surface Water PEC‟s in a small ditch adjacent to the double railway track similar

to that used in the HardSPEC Groundwater scenario. The module addresses exposure resulting from

spray drift, run-off and leaching through the railway embankment.


7

2 METHODS FOR CALCULATING PECSW RESULTING FROM SPRAY DRIFT, RUN-

OFF AND LEACHING FOLLOWING HERBICIDE APPLICATION TO A RAILWAY

In the following sections, separate methods are developed to address specific routes of herbicide loss

to surface water bodies associated with a railway. Firstly however, it is necessary to identify the most

realistic type of surface water body associated with a railway and define its characteristics.

2.1 Identification of the surface water body

In order to create a realistic worst-case situation, the surface water body associated with the railway

scenario should be relatively static and based on the small 1 metre wide ditch defined for the FOCUS

surface water scenarios (Linders et al, 2003). Such a surface water body is only likely to be present

in low-lying situations such as occur in the Fens, Humber/Trent basin or the Vale of York. It is

hydro-dynamically connected to a shallow groundwater body and water movement in the ditch is

primarily groundwater flow. In such situations, any railways present are carried on embankments and

such ditches thus usually lie alongside that embankment.

Having identified the realistic worst-case type of surface water body associated with a railway, its

characteristics and that of the associated railway are defined as follows:

1. The embankment carries a dual track railway line. Individual lines in each „standard gauge‟ rail

track are 4ft 8.5 inches (1.435 m) apart and each set of tracks is 6 ft (1.829 m) apart. The width of

the „cess‟ from the edge of each embankment to the first rail line is 5ft (1.524 m). This gives a

total width of the ballast surface of almost 7.75m.

2. The embankment is 5m high. A realistic slope for the angle of each side of the embankment is 60o,

which means that the horizontal distance from the edge of the top of the embankment to the base

of the embankment is 2.9m.

3. The embankment beneath the railway lines comprises a 0.6 m thick layer of railway ballast over a

0.3 m thick layer of artificial sandy „formation‟ material over 4.1 m of embankment material of

unspecified composition. The thickness and constituents of the railway ballast and underlying

„formation‟ are exactly as in the current HardSPEC Railway Groundwater Scenario (see

HardSPEC worksheet “Railway_scenario”).

4. The dimensions and characteristics of the surface water ditch adjacent to the embankment are

exactly the same as for the FOCUS Surface Water ditch scenario (Linders et al, 2003):

Length: 100m; Width: 1m; Water depth: 30cm; Sediment org. carbon content: 5%

Sediment bulk density: 0.8 gm cm-3

…Effective sediment depth for partitioning: 1cm;


8

5. Water flow in the ditch is controlled principally by flow in the groundwater body which is slow,

1m day-1

and at right angles to the railway line and embankment.

A plan of this basic situation is shown in Figure 2.1-1 and a cross section of the railway, its

embankment, ditch and associated groundwater body is shown in Figure 2.1-2.

Figure 2.1-1 Plan view of the idealised railway surface water catchment

Direction of groundwater flow

10

0 m

Groundwater

Bodye

mb

an

km

en

t

em

ba

nk

me

nt

Du

al

railw

ay t

rack

on

ba

llas

t

Dit

ch

1m

wid

e

2.9 m wide

embankment sides

7.75 m


10

0 m

Groundwater

Bodye

mb

an

km

en

t

em

ba

nk

me

nt

Du

al

railw

ay t

rack

on

ba

llas

t

Dit

ch

1m

wid

e


10

0 m

Groundwater

Bodye

mb

an

km

en

t

em

ba

nk

me

nt

Du

al

railw

ay t

rack

on

ba

llas

t

Dit

ch

1m

wid

e

Direction of groundwater flowDirection of groundwater flow

10

0 m

Groundwater

Bodye

mb

an

km

en

t

em

ba

nk

me

nt

Du

al

railw

ay t

rack

on

ba

llas

t

Dit

ch

1m

wid

e

em

ba

nk

me

nt

em

ba

nk

me

nt

Du

al

railw

ay t

rack

on

ba

llas

t

Dit

ch

1m

wid

e

2.9 m wide

embankment sides

7.75 m

2.9 m wide

embankment sides

7.75 m

2.9 m wide

embankment sides

7.75 m


9

Figure 2.1-2 Cross section of the idealised railway surface water catchment

2.2 Spray Drift

The issue of spray drift associated with herbicide application to railways is a difficult one because

little data exists on direct inputs from this source. Clearly, the amount of spray drift to the surface

water body depends on the method of application and the amount of railway track surface to which

herbicide is applied. Two methods are considered here:

2.2.1 Application from a ‘spray train’ mounted with the ‘Radiarc’ nozzle system.

This system was developed by J.S.D Research and Development Ltd. and is now used as a matter of

routine by the company „Network Rail‟, who are responsible for maintaining track in the UK.

When using the spray train, operators have confirmed that, in some circumstances, especially on

branch lines, both the „up‟ track and „down‟ track may be sprayed on the same day. Even on some

main lines, both „up‟ and „down lines may be sprayed within one or two days of each other. The spray

width covered by each pass of the train comprises the width of the railway track (4 ft 8.5 inches) plus

the ballast area from the edge of the track to the embankment edge (the „cess‟ area: 5ft) plus half the

distance between the two tracks (6ft / 2), giving a total spray width of 12ft 8.5 inches, equating to

3.8735 m. A realistic worst case assumption for the scenario is thus that both sets of tracks are treated

and the total application area for the spray train scenario is thus 774.7 m2 (100m length of track x

3.8735m width x 2). This situation is illustrated in Figure 2.2-1.

Surface water

ditch

Railway ballast

Railway tracks

Sandy railway „formation‟

Embankment

1 m


4 m

2.9 m

7.75 m

1 m


10

Figure 2.2-1 Illustration of spray application for the Railway surface water scenario

However, the Radiarc spray system is fitted with a „magic eye‟ technology designed to significantly

reduce the area to which spray is applied. In such cases it may be acceptable to reduce the effective

application rate (g ha-1

) but, for regulatory applications, such reductions must be supported with

data that shows the effective application rate over a 100 m length of rack.

The advantage of using the spray train as the main application method is that, in addition to it being

the most common form of application to railway tracks, there is measured data available on which to

base simulations of drift losses. The Radiarc application technology on the spray train effectively

reduces spray drift and to demonstrate this J.S.D Research and Development Ltd and Network Rail

commissioned research to investigate the amount of drift associated with its use (Parkin & Miller,

2004). The spray system is illustrated in figure 2.2-2.

1.435 m wide

1.524 m wide

0.914 m wide

100 m

Ditch 1m wide

embankment

Spray train on

„down‟ line

Spray train

on „up‟ line

Spray train

application area

embankment

1.435 m wide

1.524 m wide

0.914 m wide

100 m

Ditch 1m wide

embankment

Spray train on

„down‟ line

Spray train

on „up‟ line

Spray train

application area

1.435 m wide

1.524 m wide

0.914 m wide

1.435 m wide

1.524 m wide

0.914 m wide

100 m

Ditch 1m wide

embankment

Spray train on

„down‟ line

Spray train

on „up‟ line

Spray train

application area

100 m

Ditch 1m wide

embankment

Spray train on

„down‟ line

Spray train

on „up‟ line

100 m

Ditch 1m wide

embankment

Spray train on

„down‟ line

100 m

Ditch 1m wide

embankment

Spray train on

„down‟ line

Spray train

on „up‟ line

Spray train

application area

Spray train

application area

embankment


11

Figure 2.2-2 Illustration of the Radiarc nozzle application technology used on the Network

Rail spray train.

This shows that there are two different components of the spray: A vertical spray component directed

downwards onto the „4 foot‟ track area; A „sideways‟ component directed at an angle from the side of

the train in order to treat the cess area of ballast at the side of the track or half of the ballast area

between the „up‟ and „down‟ tracks. The commissioned research investigated spray drift from both

these spray components, using a wind tunnel in which the „sideways‟ component of the spray was

directed in the same direction as the wind. Results from this latter component (called the „cess

configuration‟) relate to drift from the spray directed towards the cess area of track whereas results

from the vertical component (called the „4 foot configuration‟) relate to drift from the spray directly

down onto the track area. In summary, the experiment produced duplicate measurements of the %

drift at three different down wind distances (2, 4 and 19 m) and three different wind speeds (12.2,

18.1 and 24.3 miles hr-1

). Percentage loss from spray drift is dependent on both wind speed and

downwind distance and for the purposes of scenario development it is thus necessary to derive a

realistic worst case situation for both these variables.

Realistic worst-case wind speed

Downward

spray onto the

„4 ft‟ track

Sideways spray

onto the „5 ft‟

cess area


12

The „Code of Practice for using plant protection products‟ (Defra, 2006) recommends (table 6, page

90) that spraying should not take place if there is a force 4 wind (Beaufort scale) and that, if possible

spraying of herbicides should be avoided if there is a force 3 wind. The spray train operators confirm

that they adhere to this code of practice and thus these wind speeds impose an upper limit on the

realistic worst-case wind speed for the scenario. According to the code of practice, Force 3 wind

relates to speeds of 4 to 6 miles hr-1

at the height of the spray nozzles assuming there is a crop

covering the ground. If there is no crop or grass cover, the wind speed at the height of the spray

nozzles will be higher and this will be the case for the spray train applications. The height of the

spray train nozzles above the track is 0.8 m and this was also the height of the nozzle used in the

experimental study. However, the scenario embankment is 5m above ground level and thus the total

height above ground for the spray train nozzles is 5.8 m. Using the Beaufort scale, force 3 wind

speeds at a height of 10 m above the ground range from 8 to 12 miles hr-1

. Given the uncertainty

related to operator‟s estimation of wind forces and the variability of wind over short periods during

application, it is likely that there will be occasions when spraying takes place at the upper range of

force 3 winds which, at a height above ground of 5.8 m will be somewhere between 6 and 12 miles

hr-1

. The latter wind speed is virtually the same as one of the wind speeds for which experimental

drift data is available and the ability to use this data, combined with the uncertainty related to wind

speed, supports the selection of a worst-case wind speed of 12 miles hr-1

for the scenario. It is

important to recognise that this is an absolute worst case for wind speed during spraying as it

represents a value at the uppermost limit of force 3 on the Beaufort scale and, to take into account

operators uncertainty in estimating wind speed, is the speed at a height of 10m whereas the actual

wind speed at the spray train nozzle height of 5.8 m will be significantly lower than this.

Realistic worst-case drift distances

The measured data for spray drift (Parkin & Miller, 2004) represents a „worst case‟ situation with

respect to wind direction which is at right angles to the direction of travel of the train and in the same

direction as the spray component directed sideways onto the cess nearest to the railway ditch (during

the „up‟ track pass of the train) or sideways onto the central half of the ballast surface between the

two tracks (during the „down‟ track pass of the train). Similarly, it represents a worst case situation

for the „4 foot‟ spray component directed downwards onto the track during both the „up‟ and „down‟

track passes of the train. However, for the spray components directed sideways onto the central half

of the ballast surface between the two tracks (during the „up‟ track pass of the train) and sideways

onto the cess furthest from the railway ditch (during the „down‟ track pass of the train), the wind

direction is directly against the direction of spray and will thus counteract the direction of spray,

significantly reducing the amount of drift (see figure 2.2-5 below).


13

In order to simplify this situation for calculation purposes, the different components of spray from the

train have been separated into six sections, each of which has a defined target area of spray and

distance from the spray nozzle to the edge of the water body. These target areas and distances were

calculated as follows

Spray section 1.

The target area is that for the nozzles mounted at the edge of the „up‟ train and directed sideways

towards the cess area nearest to the ditch. The width of the target area is thus the distance from the

edge of the train to the edge of the cess area nearest to the ditch. The train is 2.6 m wide, which, for

most lines, is the maximum allowable size for rolling stock to allow clearance under bridges and

between tracks (the „loading gauge‟) ,and the track is 1.4351 m wide so the „overhang‟ of each side of

the train beyond the rail edge is:

[2.6 – 1.4351] / 2 = 0.58245 m

The width of the target area is thus: 1.524 – 0.58245 = 0.94155 m

and the target spray area is 100 x 0.94155 = 94.155 m2

The distance from the spray nozzle to the edge of the surface water body is:

2.9 (the width of the embankment) + 0.94155 = 3.84155 m

Spray section 2.

The target area is that for the nozzles mounted below the „up‟ train and pointed directly downwards

onto the „up‟ track area. The width of the target area is thus the width of the train and the spray

section area is:

100 x 2.6 = 260 m2

The distance from the spray nozzle to the edge of the surface water body obviously varies as nozzles

are located at different points underneath the train. However, to simplify the calculations a single

point in the centre of the train is used because this represents an average of the distances of each

spray nozzles underneath the train. The travel distance for this spray section is thus:

2.9 + 0.94155 + [2.6 / 2] = 5.1455 m

Spray section 3.

The target area is that for the nozzles mounted at the edge of the „up‟ train and directed sideways

towards the ballast surface between the „up‟ and „down‟ tracks. The width of the target area is thus

half the distance between the tracks minus the „overhang‟ of the side of the train beyond the far rail

edge of the „up‟ track:

0.914 - 0.58245 = 0.33195 m, so the target spray area is:

100 x 0.33195 = 33.195 m2

And the distance from the spray nozzles to the edge of the water body is:


14

2.9 + 0.94155 + 2.6 = 6.44155 m

Spray section 4.

The target area is that for the nozzles mounted at the edge of the „down‟ train and directed sideways

towards the ballast surface between the „down‟ and „up‟ tracks. The width of the target area is thus

half the distance between the tracks minus the „overhang‟ of the side of the train beyond the far rail

edge of the „down‟ track:

[1.8288 / 2] - 0.58245 = 0.33195 m, so the target spray area is:

100 x 0.33195 = 33.195 m2

And the distance from the spray nozzles to the edge of the water body is:

2.9 + 1.524 + 1.4351 + [1.8288 - 0.58245] = 7.10545 m

Spray section 5.

The target area is that for the nozzles mounted below the „down‟ train and pointed directly

downwards onto the „down‟ track area. The width of the target area is thus the width of the train and

the spray section area is:

100 x 2.6 = 260 m2

As with spray section 2, a single point in the centre of the train is used to calculate the spray travel

distance because it represents an average of the distances of each spray nozzles underneath the train.

The travel distance for this spray section is thus:

2.9 + 1.524 + 1.4351 + 1.8288 + [1.4351/2] = 8.40545 m

Spray section 6.

The target area is that for the nozzles mounted at the edge of the „down‟ train and directed sideways

towards the cess area furthest from the ditch. The width of the target area is thus the same as that for

spray section 1: 94.155 m2

However the spray travel distance is:

2.9 + 1.524 + 1.4351 + 1.8288 + 1.4351 + 0.58245 = 9.70545 m

The critical parameters derived from these calculations and used to calculate overall spray drift from

the train are summarized in table 2.2-2.

Table 2.2-2 Spray sections, target areas and distances from spray nozzle to edge of the ditch for the

spray train application.

Spray section

number Description

Spray target

area (m2)

Distance (m) from the spray

nozzle to the edge of the ditch

1 Cess area nearest to the ditch 94.155 3.842

2 „Up track 260 5.142

3 Half of the section between the tracks 33.195 6.442

4 Half of the section between the tracks 33.195 7.105


15

5 „Down‟ track 260 8.405

6 Cess area furthest from the ditch 94.155 9.708

The overall drift scenario for the spray train passes is illustrated in figure 2.2-5.

Figure 2.2-5 Illustration of spray drift for the Railway surface water scenario

Calculation of overall spray drift loss from the spray train application

Having derived the absolute worst-case wind speed and drift distances for the spray train these can

now be used with the experimental data for the 12.2 miles hr-1

wind speed study to calculate the

percentage drift losses for each identified spray section. The measured values of the percentage drift

loss at downwind distances of 2, 4 and 19 m for both the „cess‟ and „4 foot‟ configurations have a

power relationship as shown in figure 2.2-6 below.

Spray

sections

1 2 43 65

Spray train

on ‘up’ tracksSpray train on

‘down’ tracks

3.84 m5.14 m

6.44 m7.11 m

8.41 m9.71 m

Drift

distances

Wind direction

Spray

sections

1 2 43 65

Spray train


‘down’ tracks

3.84 m5.14 m

6.44 m7.11 m

8.41 m9.71 m

Drift

distancesSpray

sections

1 2 43 65

Spray train


‘down’ tracks

Spray

sections

1 2 43 65

Spray train


‘down’ tracks

Spray

sections

1 2 43 65 Spray

sections

1 2 43 65

Spray train


‘down’ tracks

Spray train


‘down’ tracks

3.84 m5.14 m

6.44 m7.11 m

8.41 m9.71 m

Drift

distances

3.84 m5.14 m

6.44 m7.11 m

8.41 m9.71 m

3.84 m5.14 m

6.44 m7.11 m

8.41 m9.71 m

Drift

distances

Wind direction


16

Cess configuration y = 3.1314x-1.404

R2 = 0.9989

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 2 4 6 8 10 12 14 16 18 20

Distance down wind (m)

Mean

perc

en

tag

e l

oss

4 foot configuration y = 0.5424x-1.3427

R2 = 0.9959

0

0.05

0.1

0.15

0.2

0.25

0 2 4 6 8 10 12 14 16 18 20

Distance downwind (m)

Mean

perc

en

tag

e l

oss

Figure 2.2-6 Relationships between down wind distance and percentage loss for the cess and 4

foot configurations and a wind speed of 12.2 miles hr-1


17

Using these relationships the percentage loss from each 100 m long spray section can be calculated

from its down wind distance by assigning each spray section to either the „cess configuration‟ data or

the „4 foot configuration‟ data. Spray sections 1 & 4 clearly relate to the cess configuration data,

whereas sections 2 & 5 clearly relate to the 4 foot configuration. For all these spray sections, the

derived realistic worst case wind speed also applies. Spray sections 3 and 6 are more difficult to

characterize because their spray is directed into the wind (see figure 2.2-5) and there is no measured

data for such a configuration. To calculate drift from these sections therefore, the relationship for the

4 foot configuration is used even though this is clearly an over-estimate the amount of drift from

these sections.

Final calculations of percentage drift losses from the spray train are summarized in table 2.2-3.

Table 2.2-3 Calculation of realistic worst-case spray drift from the spray train application.

Spray

section

Area sprayed

(m2)

Spray travel

distance (m)

Configuration

used

Wind speed

miles hr-1

Drift potential

%

1 94.155 3.84 Cess 12 0.47

2 260 5.14 4ft 12 0.06

3 33.195 6.44 4ft 12 0.04

4 33.195 7.11 Cess 12 0.20

5 260 8.41 4ft 12 0.03

6 94.155 9.71 4ft 12 0.03

Overall 774.7 0.10

2.2.2 Localised application by a hand-held sprayer along the edge of the railway track nearest to the surface water body.

This application method is included in the module to account for the few situations where there is ad-

hoc use of hand held sprayers to control localised weed infestations. In the proposed scenario, the

horizontal distance from the edge of the railway track to the edge of the ditch is 2.9 m but the track

surface is 5m above the surface of the ditch which means that the effective distance used to estimate

spray drift losses is likely to be less. As with the HardSPEC Urban and Major Road scenarios

therefore a value of 2.8% drift loss is used, based on the 90th

percentile highest value for a hand held

application to a crop < 50 cm high and at a distance of 1 m from the edge of the 'crop' to the start of

the water body, derived from the BBA (2000) measured data.

As a first tier assessment, there is a default assumption that the spray is applied as a continuous 1m

wide swath along the 100 m of track edge. Such an assumption represents an unrealistic worst-case

because hand-held sprayers use spot-applications rather than swath-application and the scenario thus

combines an unrealistically large application loading with estimated worst-case losses from measured


18

data. It is also recognized that other types of application method may be used on an ad-hoc basis and,

in order to investigate such methods or a range of more realistic application loadings from hand-held

sprayers, users can change both the percentage loss from ad-hoc application and the fraction of 100

m2 target area of track to which spray is applied. For regulatory applications, any changes to the

default percentage drift loss resulting from different application methods or reductions in the

fraction of track treated must be supported with data to justify the values used.

2.2.3 Fate in the surface water body

Inputs to the railway ditch from spray drift occur on the day of application and all go into the aqueous

phase. At this stage therefore there is no herbicide mass in the ditch sediment phase.

During this first day, partitioning occurs between water and sediment phases of the ditch but, as with

the „STEPS1-2 in FOCUS‟ model, only 2/3 of the spray drift inputs are available for partitioning, the

remaining 1/3 stays in the ditch water phase. This is because some of the inputs from spray drift

remain in the upper parts of the water column and are too far away from the sediment to be subject to

sorption forces. The figure of 1/3 is a calibrated number based on experimental observations

(Linders et al (2003) and is intended as a „first tier‟ approach. A possible second tier approach to this

would be to use specific water partitioning kinetic data from experimental studies using aerial

deposition inputs but this could only be done if the model was to be specifically adapted by changing

the calculations in the worksheet “Losses_AR”.

Following partitioning, masses of herbicide in both the water and sediment phases are calculated

using values for soil Koc, water depth (30 cm), effective sediment depth (1 cm), sediment bulk

density & organic carbon content exactly as in the existing HardSPEC stream model. They represent

the final masses present in the water and sediment phases of the ditch at the end of the first day.

However, as with all the other surface water modules in HardSPEC, PECsw on the day of application

is calculated from the mass of herbicide in the ditch before partitioning occurs.

2.3 Run-off

Run-off directly from Railway track formations is not likely as the ballast that forms the main part of

the formation upon which railway tracks are placed is very permeable. However, if an impermeable

layer underlies the formation, any excess rain water reaching that layer will percolate sideways and

run off down the embankment to the adjacent ditch, as illustrated in figure 2.3-1 below. The amount

of such runoff and the extent of attenuation of herbicide loads during transport down the embankment

are uncertain as no data are available on such a specific subject.


19

2.3.1 Run-off simulation

In order to simulate this scenario, the daily mass lost (mg) per 0.492 m² of ballast (calculated by the

ballast leaching model in the worksheet “masses lost per 0.5 mm rain”), which is input to cells F100

to F172 of the worksheet “losses_AR” in HardSPEC v. 1.1, are converted into a daily total load ( g)

lost from the ballast based on the application area associated with the Network Rail spray train

mounted with the „Radiarc‟ nozzle system (see section 2.2.1 above). However, although all 774.7 m2

of the track receives spray which is then subject to leaching through the railway ballast, not all of the

leached mass will move laterally to the side of the embankment nearest to the surface water ditch.

This is because some of the mass leached from ballast area furthest from the ditch will move to its

nearest embankment side. In this runoff scenario there is a worst case assumption that all the

herbicide mass leached from spray sections 1 to 5 (see figure 2.2-4) moves to the ditch side of the

embankment and is lost through runoff, giving a total contributing area of 100 x 6.81 = 681

m2, representing 88% of the total mass leached through the railway formation.

For the runoff scenario therefore, the total daily load ( g) lost from the ballast application area

= daily mass (mg) lost per 0.492 m² of ballast x 1000 x 681 / 0.492.

This mass is then used as a direct input to the surface water body but, because the amount of

attenuation that may occur during run off is uncertain, the mass is first multiplied by an attenuation

factor. This factor is specified by the user as an additional input parameter in cell C21 of the

worksheet “Herb_props”. The default value in this first tier version of the module is 1, i.e. there is no

attenuation of loads during transport down the railway embankment which is clearly very

conservative and probably unrealistic. However, it can be changed by the user to a smaller

fraction, providing the change is based on a justified argument.


20

Figure 2.3-1 Pesticide transport pathways to the railway surface water body for a runoff

scenario


The dynamics of herbicide fate in the Railway ditch are based, as far as possible on the fate dynamics

developed for the surface water bodies in the „STEPS1-2 in FOCUS‟ model for predicting PECsw for

the European registration process (Linders et al 2003). However, some minor adjustments have been

made to take into account the fact that the „STEPS1-2 in FOCUS‟ water body is static, whereas in the

railway ditch water moves laterally at a rate of 1m day-1

(see section 2.1 above). This simple

approach to surface water fate dynamics ensures a similar „tier 1‟ worst-case approach to that adopted

for EU registration purposes.

Daily run-off input loads to the surface water body occur from the first day after application. As in

the existing HardSPEC stream and pond water bodies, loads are added already partitioned between

water and sediment. The input load in sediment and water is added to any residual loads remaining in

the ditch sediment from the previous day and the calculated total load re-equilibrates between

aqueous & sediment phases to give a final aqueous and sediment phase load at the end of the day

time-step. Partitioning is calculated using values for soil Koc, water depth (30 cm), effective

sediment depth (1 cm), sediment bulk density & organic carbon content exactly as in the existing

HardSPEC stream model. These „final‟ masses are used to calculate concentrations in the ditch water

and sediment phases.

Residual sediment loads are calculated using the final sediment phase loads from the previous day

and the herbicide half life in sediment, which is derived from the model input data. No aqueous phase

4 m

2.9 m

Impermeable layer

Spray drift

Herbicide run-off with specified attenuation

Herbicide applied via spray train with

„Radiarc‟ nozzles

Herbicide transport

with attenuation

6.81 m

1 m

Surface waterditch

1 m


4 m

2.9 m

Impermeable layer

Spray drift




Herbicide transport

with attenuation

6.81 m

1 m

Surface waterditch

1 m


4 m

2.9 m

Impermeable layer

Spray drift




Herbicide transport

with attenuation

6.81 m

1 m

Surface waterditch

1 m


4 m

2.9 m

Impermeable layer

Spray drift




Herbicide transport

with attenuation

6.81 m

1 m

Surface waterditch

1 m


4 m

2.9 m

4 m

2.9 m

4 m

2.9 m

4 m

2.9 m

Impermeable layer

Spray drift




Herbicide transport

with attenuation

6.81 m

1 m

Surface waterditch

1 m


Impermeable layer

Spray drift




Herbicide transport

with attenuation

6.81 m

1 m

Surface waterditch

1 m

Impermeable layer

Spray drift




Herbicide transport

with attenuation

6.81 m

1 m

Impermeable layerImpermeable layer

Spray drift




Herbicide transport

with attenuation

Spray drift




Herbicide transport

with attenuation

6.81 m

1 m

6.81 m

1 m

Surface waterditch

1 m

Surface waterditch

1 m1 m



21

residual loads remain from the previous day because flow in the ditch is determined by the

groundwater flow rate of 1 m day-1

. This flow is at right angles to the 1 m wide ditch and thus an

equivalent volume of each day‟s input water flows out of the ditch thus keeping its water depth static

and removing any aqueous phase loads that are present at the end of the time step.

Calculated final masses in the ditch aqueous and water phases are then used to calculate

concentrations in the ditch water and sediment phases, exactly as in the existing HardSPEC model.

2.4 Leaching

If there is no impermeable layer below the railway formation, then any herbicide loads that leach out

of it will continue to leach vertically to the underlying groundwater body. The rate of such leaching

and the amount of attenuation that occurs during that leaching is very much dependent on the nature

and characteristics of the embankment material. As the purpose of this study is to undertake a worst

case approach to exposure assessment, a set of worst-case assumptions are made with respect to

herbicide application and fate of residues following leaching out of the railway formation. These

assumptions are described in the following sections and illustrated in Figure 2.4-1 below.

2.4.1 Herbicide application, interception by plants and spray drift

As a realistic worst-case for leaching, it is assumed that herbicide is applied at a recommended rate to

the entire 774.7 m2 of track and ballast area associated with „up‟ and „down‟ track passes of the

Network Rail spray train mounted with the „Radiarc‟ nozzle system (see figure 2.2-1 above).

Of the herbicide sprayed onto the railway line, 10% is intercepted by growing plants exactly as

described in the existing HardSPEC railway scenario. The amount of spray drift losses associated

with use of the spray train are described in section 2.2.1 and, as a result of this, a further 0.68% of the

applied mass is not deposited on the application area.


22

Figure 2.4-1 Pesticide transport pathways to the railway surface water body for a leaching

scenario

2.4.2 Leaching through the railway formation

Herbicide reaching the railway line surface is then leached through the railway ballast and the

underlying „sandy formation‟, using the mechanisms and model algorithms exactly as in the existing

HardSPEC Railway Scenario (Hollis et al 2004).

2.4.3 Transport through the railway embankment

The daily loads calculated as leaching out of the base of the railway formation are then assumed to

by-pass directly through the railway embankment to the groundwater surface with no further

attenuation. This is a first tier assumption and provides an absolute worst case situation for leaching

because, in reality, some attenuation is likely to occur as a result of dispersion, sorption and

degradation during transport through the embankment, even if by-pass flow occurs.

2.4.4 Transport in the saturated zone

Once the leached herbicide load reaches the groundwater surface it is transported laterally to the

surface water ditch adjacent to the railway embankment. This transport is modelled using the same

one-dimensional slug-injection groundwater model of Crank (1956), where herbicide residues are

attenuated through partitioning and longitudinal dispersion, as in the current HardSPEC railway

scenario. However for this study, it is necessary to change the groundwater flow velocity to 1m day-1

in order to simulate the slow moving groundwater body. In addition, it is necessary to identify a

Surface water

ditch

1 m

Spray drift

Herbicide transport with

groundwater dispersion

Points of herbicide „injection‟

into groundwater

1m

3.4 m

Herbicide transport

with no attenuation

10.4 m

1 m

7.747 m

Herbicide transport

with attenuation

Herbicide applied via spray

train with Radiarc nozzles


4 m

2.9 m

Surface water

ditch

1 m

Spray drift




into groundwater

1m

3.4 m

Herbicide transport

with no attenuation

10.4 m

1 m

7.747 m

Herbicide transport

with attenuation




4 m

2.9 m

Surface water

ditch

1 m

Spray drift




into groundwater

1m

3.4 m

Herbicide transport

with no attenuation

10.4 m

1 m

7.747 m

Herbicide transport

with attenuation



Surface water

ditch

1 m

Surface water

ditch

1 m

Spray driftSpray drift




into groundwater

1m

3.4 m

Herbicide transport

with no attenuation

10.4 m




into groundwater

1m

3.4 m

Herbicide transport

with no attenuation

10.4 m

1m

3.4 m

Herbicide transport

with no attenuation

10.4 m3.4 m

Herbicide transport

with no attenuation

10.4 m

1 m

7.747 m

Herbicide transport

with attenuation



1 m

7.747 m

Herbicide transport

with attenuation

1 m

7.747 m

Herbicide transport

with attenuation



Direction of groundwater flowDirection of groundwater flow

4 m

2.9 m2.9 m


23

suitable „point of injection‟ for leached herbicide loadings into the groundwater body in order to

calculate the distance of travel to the surface water ditch.

Herbicide residues leaching from the railway formation are likely to reach the groundwater surface at

any point along the width of the area to which herbicide is applied and thus each point of herbicide

injection will have a different travel distance. In order to simplify the groundwater modelling, eight

„points of injection‟ have been used, associated with the mid-point of each 1m section of track across

the 7.747 m width of the ballast surface that receives herbicide from the spray train. A 1m section

was used because this equates with the daily rate of groundwater flow and thus represents the daily

input to the water body from each 1m strip of track surface.

The eight points of injection are thus 0.5, 1.5, 2.5, 3.5, 4.5, 5.5 6.5 & 7.5 m from the upper edge of

the embankment nearest to the surface water ditch and each one has a different groundwater travel

distance associated with it. As indicated in section 2.1 above, the horizontal distance from the upper

surface of the embankment to the top of the ditch bank is 2.9 m, and the groundwater travel

distances used in the groundwater fate model are thus 3.4, 4.4, 5.4, 6.4, 7.4, 8.4, 9.4 & 10.4 m. These

distances are used in the Crank groundwater model to calculate daily inputs to the surface water ditch

resulting from each of the eight points of injection of herbicide residues into the groundwater body.

2.4.5 Calculation of total loadings flowing into the ditch

Daily total loads flowing into the ditch from the groundwater body are calculated from the daily

inputs to the surface water body from each of the eight points of groundwater injection across the

width of the railway track. The Crank groundwater model calculates the daily input loads associated

with herbicide impacting on a single 0.492 m2 of railway ballast surface. The area associated with the

eight calculated input loads is therefore 8 x 0.492 = 3.936 m2 and in order to calculate

the total load input to the 100 m length of ditch, it is necessary to multiply the calculated load by the

number of 3.936 m2 areas in the 774.7 m

2 of sprayed track. This equates to 196.824 areas of 0.492 m

2

and the total daily load of herbicide residues flowing into the ditch is thus:

[18 Daily load from injection point n] x 196.824)


Daily input loads from the groundwater body to the ditch occur from the first day after application.

Once input to the ditch, their fate is calculated in exactly the same way as that of the run-off input

loads described in section 2.3.2 above thus ensuring a similar „tier 1‟ worst-case approach to that

adopted for EU registration purposes.


24

2.5 Summary of „worst-case‟ assumptions in the methodology

Firstly, it should be noted that the methods for run-off and for leaching described above are „mutually

exclusive‟ worst-cases because each one assumes that ALL of the herbicide leaching out of the base

of the railway formation following application, contributes EITHER to run-off down the railway

embankment to the surface water body, OR to leaching through the unsaturated zone to the

underlying shallow groundwater body and thence to the surface water ditch.

In addition, the following „worst-case‟ assumptions are incorporated:

2.5.1 Rainfall patterns

Significant rainfall (5mm) occurs on the day after application.

A 75th percentile wettest spring rainfall sequence follows application.

2.5.2 Herbicide application

There is a maximum spray target area for leaching and run-off simulation because both „up‟

and „down‟ sets of tracks are sprayed.

There is a large spray target area for local hand-held application: A 1m wide swath.

As a first tier assessment it is assumed that herbicide is applied to 100% of the target area.

2.5.3 Spray drift

Drift from the spray train is based on the worst-case wind direction which is in the same

direction as that of the sideways pointing nozzles nearest to the ditch.

The amount of drift from the spray train is based on experimental data and an absolute worst-

case wind speed of 12 miles hr-1

derived from recommendations in the code of practice for

using plant protection products (Defra, 2006).

The 90th percentile largest losses for most ground applied sprays (2.8 %) from the

FOCUS_SW EU drift calculator are used to calculate spray drift from local hand-held

applications.

2.5.4 Run-off

88% of the total load leaching out of the railway formation contributes to run-off.

As a first tier assessment it is assumed that there is no attenuation of herbicide loads during

run-off to the surface water body.

2.5.5 Leaching

There is no attenuation of loads leached out the railway formation during transport in the

unsaturated zone.

Transport in the saturated zone only considers attenuation from partitioning and longitudinal

dispersion.


The surface water body is a small 1m wide ditch directly next to the railway embankment and

with characteristics similar to those of the FOCUSsw ditch.

Fate dynamics in the ditch are similar to those used in the „STEPS1-2 in FOCUS‟ exposure

assessment, except that all of the previous day‟s residual aqueous phase mass is lost by

groundwater turnover. The railway ditch is not static.


25

3 ADAPTION OF THE HARDSPEC MODEL (V. 1.2.1) TO INCORPORATE THE NEWLY

DEVELOPED RAILWAY SURFACE WATER EXPOSURE MODULE.

In order to incorporate the methods developed and described in section 2 the following modifications

to the existing HardSPEC model (v. 1.2.1) were implemented.

3.1 Worksheet “Herb_props”

Cells B20 to C22 have been added to enable a user to specify what fraction of the full 774.7 m2 of

railway track application area actually has herbicide applied to it by the spray train and what

attenuation factor is applied to the run-off from railway formations (see section2.3.1). The default

values for both of these are 1 and are already inserted in cells C21 & C22. These values can be

changed by the user providing such a change is based on a justified argument.

Cells B25 to C29 have been modified to enable the user to examine the surface water exposure in the

Railway ditch resulting from application by a hand-held sprayer. Because the application method is

used in a very limited context and results in loads to the railway track that are potentially much less

than those from the spray train applications, it is not necessary to incorporate spray drift inputs from

hand held applications into the main surface water exposure calculations in the worksheet

“losses_AR” which use spray drift inputs only from the spray train application method. However, to

ensure that all possible contamination routes are covered, equations have been added to cells C29 and

C30 to calculate the PECsw resulting direct from spray drift from the hand-held application method.

This can then be compared with the predicted exposure data from the main module to identify the

worst-case situation. The user inputs for this calculation are in cells C27 and C28 which specify the

percentage of the applied amount impacting as spray drift and the fraction of the 100m2 target area of

track to which spot spray is applied. The drift input mass resulting from such a fraction is shown in

Cell C29 and the resulting surface water concentration in the ditch shown in cell C30. It is

important to note that users should only change the values in cells C27 and C28.

The format of the modified input data worksheet “Herb_props” is shown in figure 3.1-1 below.


26

Herbicide properties

Herbicide name atrazine

% of applied amount impacting as spray drift. Urban & Major road 2.8

Measured Kp asphalt (mg m-2

) 2.53

Measured Kp concrete (mg m-2

) 1.280

soil koc (mL g-1

) 100

solubility (mg L-1

) 33

Specific Gravity 1.23

DT50 in soil (days) 50

DT50 on hard surfaces (days) not known

DT50 in sediment (days) 50

DT50 in water (days) 2

Application amount (g/ha)

urban 3000

Road 3000

Railway 3000

Uncertainty factors

Fraction of 400 m2

railway track target area actually sprayed 1

Run-off attenuation factor applied to leached load from ballast 1

% of applied amount impacting as spray drift. 2.8

Fraction of 100m2 target area spot sprayed 1

Input mass(g) from hand-held spot spraying 0.8400

Concentration ( g l-1

) in water phase 28.0000

These cells can be used to examine the surface water exposure in the Railway ditch

resulting from application by a hand-held sprayer.

Users must only change the percentage drift loss and/or fraction of target area

sprayed and values less than the defaults of 2.8 and 1 must be supported by

justified argument.

Figure 3.1-1 Modified input data worksheet “Herb_props” for HardSPEC 1.3.3

3.2 Worksheet “OUTPUT”

Two new lines have been added to the „Acute Concentrations‟ table (cells A10 to E11) to show the

peak daily concentrations in water and sediment in the railway ditch resulting from a „leaching

scenario‟ (see section 2.4) and a „run-off scenario‟ (see section 2.3) respectively. In addition, the

daily PEC results for the ditch water and sediment phases have been added to the graphics showing

„water concentrations‟ and „sediment concentrations‟ for both the “leaching” and “runoff” scenarios.

These are derived from cells BF12 to BG119 and BI12 to BP119 in the worksheet “Losses_AR”.

Finally, a new set of cells, F5 to F11 have been added to show the Surface Water PEC resulting from

spray drift on the day of application. These data are derived from cells AO16, AW16, AP16, BF16 &

BO16 in the worksheet “Losses_AR”.


27

3.3 Worksheet “Railway_scenario”

The values in cells C8 to C9 have been changed to 0.07749 to reflect the changed surface area of the

scenario and the area to which herbicide is applied.

3.4 Worksheet “Losses_BR”

The railway component of this worksheet has been comprehensively modified. The contents of cells

G7 to I10 have been removed and cells G7 to N19 added in order to calculate the amounts of

herbicide applied to the track, the amounts intercepted by plants and the amounts lost to the surface

water body by spray drift. The equations in cells J11 to J16 which calculate the amount of herbicide

sprayed (g) on the different spray sections of the railway track include a multiplier referring to cell

C21 in worksheet “Herb_props”, to account for the fraction of the railway track application target

area to which herbicide is applied from the spray train with „Radiarc‟ nozzles. This automatically

reduces the average surface loading when the user changes the fraction in the “Herb_props”

worksheet. The modifications to the railway component of this sheet are shown in figure 3.2-1.

RAILWAY

Cess section of track nearest to ditch 94.155 28.2465 2.82465 3.84155 0.47 0.1336768

'Up' section of track 260 78 7.8 5.14155 0.06 0.0469492

Up' line central section of track 33.195 9.9585 0.99585 6.44155 0.04 0.0044288

Down' line central section of track 33.195 9.9585 0.99585 7.10545 0.20 0.0198746

'Down' section of track 260 78 7.8 8.40545 0.03 0.0242665

Cess section of track furthest from ditch 94.155 28.2465 2.82465 9.70545 0.03 0.0072447

Totals 774.7 232.41 23.241 0.2364405

Amount reaching surface (g) 208.933

Overall % of application impacting as spray drift 0.10

Drift

potential

Amount of

herbicide

sprayed (g)

Section of track to which spray is applied Drift loss

Amount

intercepted by

plants (g)

Distance to

water body

m

Area

sprayed

m2

Figure 3.2-1 Modification of the Railway component of worksheet “losses_BR”.

3.5 New Worksheet “Railway_surface_water”

A new worksheet “Railway_surface_water” has been added before the existing worksheet

“Losses_AR”.

This worksheet calculates transport and dispersion in groundwater moving from each of the four

„groundwater injection points‟ below the surface of the railway track to the surface water ditch. The

calculations are based on the Crank (1956) „one dimensional slug injection‟ model. Fixed model

input values are given in cells A1 to G19, whilst calculations related to each of the eight groundwater

injection points are given in cells L5 to CL2945. Summed daily loads for each of the six sets of

model data are given in cells K5 to K369.


28

3.6 Worksheet “Losses_AR”

Additional calculations have been added to this spreadsheet in order to calculate the daily and

cumulative daily masses leached out of sandy formation using the attenuation factor model applied to

the calculated daily masses leached out of the overlying ballast. These calculations have been added

in cells J98 to K172, adjacent to the existing HardSPEC attenuation factor calculations for the

unsaturated zone component of the railway groundwater module.

New routines for calculating the daily water and sediment phase concentrations in the railway surface

water ditch have been added. Those in cells AZ12 to BG119 are calculations relating to the „Leaching

scenario‟ whilst those in cells BI12 to BP119 relate to the „Run-off scenario‟. They cover daily input

masses to the surface water body (cells AZ12 to BA119 and BI12 to BJ119), daily residual masses in

the surface water body (cells BB12 to BC119 and BK12 to BL119), final masses in the surface water

body (cells BD12 to BE119 and BM12 to BN119) and daily concentrations in the surface water body

(cells BF12 to BG119 and BO12 to BP119).


29

4 EVALUATION OF RESULTS FROM THE NEW RAILWAY SURFACE WATER

MODULE

The adapted version of the HardSPEC model described in section 3 which implements the methods

developed and described in section 2, was run for the six „test compounds‟ used in the laboratory and

field monitoring studies used to develop HardSPEC. Basic physico-chemical characteristics and

application rates for these compounds are shown in table 4.0-1.

Table 4.0-1 Basic properties of the six Hard Surface „test compounds‟.

Herbicide name atrazine diuron oryzalin oxadiazon isoxaben glyphosate

soil koc (mL g-1

) 100 218 625 3200 767 28000

solubility (mg L-1

) 33 36.4 2.4 10 1.5 116000

DT50 in soil (days) 50 100 63 60 105 47

DT50 in sediment (days) 50 100 63 60 105 47

DT50 in water (days) 2 2 2 2 2 10

Application amount (g ha-1

) 3000 2700 1730 4500 75 1800

4.1 Comparison of PECsw simulations using the new railway module with other

HardSPEC surface water modules

Peak 24 hour aqueous phase PECsw results are shown in table 4.1-2 along with the aqueous phase

PECsw that results from spray drift on the day of application. Time series of daily PECsw for the

aqueous phase in the railway ditch are compared with those of the urban and major road stream

scenarios in Appendix 1.

The results indicate that except for the most mobile test compounds atrazine and diuron, peak daily

aqueous phase PECs in the railway ditch are the result of spray drift on the day of application. This

contrasts with the stream scenarios where only the most strongly sorbed compounds oxadiazon and

glyphosate have peak daily aqueous phase concentrations resulting from spray drift.


different for the leaching and run-off situations and in general run-off gives slightly higher

concentration peaks than leaching. However, such differences decrease significantly with increasing

compound sorption and, for the least mobile compounds, oxadiazon and glyphosate, leaching and

run-off inputs are so small that daily aqueous phase concentrations depend almost entirely on residual

masses from spray drift inputs on the day of application. It is important to note that for glyphosate,

this is unlikely to reflect its true behaviour in the ballast environment where work reported by


30

Strange-Hansen et al (2004) and described in section 4.2 below, indicates it is better to use Kd values

in the range of 62 – 87 ml g-1

to simulate glyphosate sorption in railway formations.

Table 4.1-2 Comparison of aqueous phase PECsw estimated for the different HardSPEC scenarios

Compound

Urban 1 Major road Railway ditch

stream pond stream leaching run-off

Peak 24 hour PECsw aqueous

phase ( g l-1

)

atrazine 307.1 26.7 154.11 15.67 42.91

diuron 244.5 21.4 115.14 7.09 15.39

oryzalin 68.2 6.0 28.94 4.54 4.54

oxadiazon 52.6 4.7 29.32 11.82 11.82

isoxaben 7.6 0.7 2.97 0.20 0.20

glyphosate 16.5 1.3 11.73 4.73 4.73

Aqueous phase PECsw from spray drift on the day of

application ( g l-1

)

atrazine 27.52 0.173 19.55 7.88 7.88

diuron 24.77 0.16 17.59 7.09 7.09

oryzalin 15.87 0.10 11.27 4.54 4.54

oxadiazon 41.28 0.26 29.32 11.82 11.82

isoxaben 0.69 0.004 0.49 0.20 0.20

glyphosate 16.5 0.10 11.73 4.73 4.73

1 The Peak PECsw is estimated using the 1.2.3 version of HardSPEC that corrects the error in urban

application identified on 21/05/2010 and includes the revised routing of hard surfaces runoff

recommended in the report on „Development of a Home & Garden scenario for HardSPEC (Hollis

& Ramwell, Sept. 2010).

Note: PECsw values in bold italics indicate where the acute 24 hour concentration is the result of

spray drift

4.2 Comparison of the surface water module results with measured data

Two „field‟ monitoring studies have been carried out to monitor environmental concentrations

resulting from herbicides applied to railway track formations (Heather et al, 1999; Ramwell et al,

2001) but only the first of these is applicable to surface waters. The objectives of this study were to

monitor the concentrations of herbicides leaching from a real railway track bed to the base of the

„soil‟ formation directly beneath it and to specially created surface trenches dug into the ballast

formation in the „cess‟ area directly adjacent to the track. Six herbicides (atrazine, diuron, oxadiazon,

glyphosate, oryzalin, isoxaben) were applied separately, via a knapsack sprayer to 250 m2 of a former

railway test track. All rail tracks at the site had been removed and only the ballast for a single track

was still in place. Sampling of drainage waters from the ballast and formation was carried out from

three separate trenches labelled „upper‟, „middle‟ and „lower‟ according to their location on the

gradient and water that collected in them was „grab‟ sampled using HDPE bottles. Water samples

from the trenches were collected on 9 occasions between 4 and 81 days after herbicide application,

normally in response to specific rainfall events. In addition, samples from the „soil‟ formation


31

beneath the railway ballast adjacent to the „middle‟ and „lower‟ surface water trenches were taken for

analysis 33 days after application and from the „soil‟ formation adjacent to the „upper‟ trench 83 days

after application. There was a small rainfall event of 0.4mm on the first day after application and a

more significant rainfall event of 4 mm on the second day after application. Subsequent rainfall was

unusually large for the time of year. 25 days after application, 81.8 mm of rain had fallen on the site

whilst by the end of the study, 83 days after application, a total of 153 mm of rain had fallen.

The conditions of this study are thus analogous to the „Runoff‟ component of the new Railway

module because the measured concentrations relate to leachate moving laterally over the

impermeable layer at the base of the railway formation. However, before any comparison of such

measured data with model predictions can take place, there are a number of issues that need to be

addressed.

Firstly, some of the HardSPEC railway scenario characteristics defined in this report need to be

modified to match those of the field study. Thus, the newly developed railway ditch model was

modified so that the amount of herbicide applied and the subsequent rainfall pattern matched those of

the study and there was no input to the surface water ditch from spray drift.

Secondly, the limitations of the railway field study mean that it is not possible to directly compare

measured concentrations with model predicted concentrations in the railway ditch because the

measured data represent effective concentrations leaching from the base of the ballast formation. It is

however possible to take the model predicted loads leaching out of the base of the railway formation

and convert them to a concentration using the area of railway track involved in the sampling and the

daily rainfall values during the study period. Even so there remain a number of uncertainties with

such a comparison:

There are only measured data for grab samples taken from the ballast trenches on 9 days of the 83 day

study period, in contrast to the continuous daily data produced by the model. For these days, analysis

produced quantifiable measurements only for atrazine, diuron and glyphosate. Oryzalin, oxadiazon

and isoxaben were detected in some of the samples but only at concentrations below the

quantification level and similar to the detections identified in the control samples taken before

herbicides were applied. This means that they are of little use for comparison purposes. In addition

there is no data available for the organic component of any fine material in the ballast from the

railway study so the default values of ballast organic matter in the current HardSPEC railway

scenario have to be used for model simulation. Water fluxes within the railway ballast and underlying

formation during the sampling period are not known but are likely to be very different from the

simple assumptions of daily drainage used in the model. The ballast leaching model produces daily

loads leaching out of the ballast per unit area and these are then reduced during transport through the


32

underlying sandy formation using an attenuation factor model. The assumption is that the ballast and

underlying formation remain unsaturated in all parts. This contrasts with the likely hydrological

dynamics in the ballast and formation during the field study where the lower parts are likely to

remain saturated for a few days after rainfall. It is thus not likely to be valid to compare the measured

concentration for a specific day with the predicted concentration for that day. The contrast is

highlighted by the fact that the limited number of measured concentrations suggest a time lag in

herbicide break through to the trenches with an apparent peak occurring 6 days after application,

whereas the model predicts an „instantaneous‟ break through peak on the day of the first rainfall

event after application (day 1). In order to match the study conditions as closely as possible therefore,

a further modification was made to the model.

Because the sandy formation is assumed to be effectively saturated for most of the time, the

attenuation factor model is not considered appropriate and instead the daily loads leaching out of the

ballast per unit area were partitioned between the aqueous and solid phases of the saturated sandy

formation using the relevant default organic carbon content, bulk density and hydraulic property

values from the model. The aqueous phase loads were then converted to concentrations using the

volume of daily rain falling on the ballast per unit area.

In addition, it is known that glyphosate is not principally sorbed to organic matter and so Koc values

are of little use for determining partitioning in railway ballast leaching. However, a study reported by

Strange-Hansen et al (2004) measured sorption of glyphosate in different types of gravel and relevant

measured Kd data from this study was therefore used to simulate glyphosate partitioning in the ballast

and underlying sandy formation. The data used is shown in table 4.2-1.

Table 4.2-1 Measured Kd values used to simulate glyphosate partitioning in the railway ballast and

underlying sandy formations (after Strange-Hansen et al, 2004).

Railway

surface type

Gravel type from Strange-

Hansen et al, 2004

% volume of

stones (>2mm)

% volume of fines

(<0.063 mm)

Kd (ml g-1

)

+ s.d.

Ballast 2/8 83 0.45 87.1 + 12.0

Sandy

formation 0/4 18 1.09 62.1 + 9.6

In order to address the contrast in timing of break through concentrations between the measured and

predicted data, a modified version of the model results was produced. This was done by setting the

predicted time series of concentrations (starting on the first day after application) to start on the 6th

day after application, so matching the apparent timing of the measured peak. Concentrations for the

first five days were then set to 0 and, for each day after application, a „forward three day running


33

average‟ concentration calculated. This procedure attempts to give an integration of the daily

predicted data that better reflects the measured data.

Comparisons of the measured and predicted (for both the modified and unmodified model results)

peak concentrations of all six test compounds from the railway field study are given in table 4.2-2,

whereas the time series of measured and predicted concentrations are shown graphically in figures

4.2-1 (based on the unmodified version of the model results) and 4.2-2 (based on the modified 3 day

running average version of the model results). For the field study data, the mean value and range for

the three samples taken on each sampling date are given.

Table 4.2-2 Measured peak concentrations ( g l-1

) in the ballast trenches from the railway field

study compared with predicted peak concentrations leaching out of the base of the

ballast from the modified HardSPEC railway model.

Compound Railway study Peak Concentration (day 6) Mean value (range)

Predicted concentrations in railway ballast leachate Unmodified daily peak Peak 3 day running average

Atrazine 1097 (860 – 1280) 1316 1082

Diuron 133 (60 – 210) 164 136

Oryzalin <10 10.6 7.0

Oxadiazon <20 1.24 1.06

Isoxaben <10 0.50 0.41

Glyphosate 12.4 (6.7 – 15.3) 15.8 11.0

Table 4.2-2 shows that, for the three compounds where meaningful comparisons can be made

(atrazine, diuron & glyphosate), the measured peak concentrations compare well with the predicted

peak concentrations for the unmodified daily model results and even better for the modified 3 day

running average values. For oryzalin, oxadiazon and isoxaben, where all samples were analysed as

being either just above or below the level of detection, peak concentrations were also predicted to be

very near to or below the level of detection. This is encouraging as it suggests that the ballast

leaching component of the new surface water runoff scenario is producing peak concentrations that

are similar to the limited measured data available.


34

Atrazine concentrations

0.00

200.00

400.00

600.00

800.00

1000.00

1200.00

1400.00

1600.00

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Days after application

Co

nc

en

tra

tio

n

g l

-1

Unmodified

model daily

values

Measured

average and

range

Diuron concentrations

0

50

100

150

200

250

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90


Co

nc

en

tra

tio

n

g l

-1

Unmodified

model daily

values

Measured

average and

range


35

Glyphosate concentrations

0

2

4

6

8

10

12

14

16

18

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90


Co

ncen

trati

on

g

l-1 Unmodified

model daily

values

Measured

average and

range

Figure 4.2-1 Measured concentrations of atrazine, diuron and glyphosate from the railway field

study compared with predicted daily concentrations using the unmodified ballast sub-

model from the modified HardSPEC railway scenario.


36

Atrazine concentrations

0.00

200.00

400.00

600.00

800.00

1000.00

1200.00

1400.00

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90


Co

nc

en

tra

tio

n

g l

-1

Modelled 3 day

running average

Measured

average and

range

Diuron concentrations

0.00

50.00

100.00

150.00

200.00

250.00

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90


Co

nc

en

tra

tio

n

g l

-1

Modelled 3 day

running average

Measured

average and

range


37

Glyphosate concentrations

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90


Co

nc

en

tra

tio

n

g l

-1

Modelled 3 day

running average

Measured

average and

range

Figure 4.2-2 Measured concentrations of atrazine, diuron and glyphosate from the railway field

study compared with predicted 3 day running average concentrations using the

modified ballast sub-model results from the modified HardSPEC railway scenario.

It is difficult to undertake a robust statistical comparison of the patterns of predicted concentrations

for atrazine, diuron and glyphosate in figures 4.2-1 and 4.2-2 with the measured data because the

latter contain only 9 values with only two sets of samples on consecutive days. It is therefore

impossible to know whether the apparent peaks in the measured data represent real peaks in the daily

concentration pattern. Also, as discussed previously, the timing of model predicted herbicide

breakthrough and that apparent from the measured data is different (see figure 4.2-1). However, the

modified 3 day running average version of the model results (see figure 4.2-2) shows a good fit to the

measured data, at least up to about 12 days after application (up to 40.2 mm accumulated rain). For

atrazine and glyphosate, predicted concentrations after day 12 appear to be under-estimated. This

does not seem to be the case for diuron although the predicted concentrations after day 12 are at the

lowest end of the measured data range.


38

5 CONCLUSIONS

Methodologies have been developed to calculate the aquatic PEC‟s in surface water resulting from

the application of herbicides to railway track formations. The methodologies cover losses from spray

drift (based on measured data), run-off and leaching and incorporate a number of realistic worst-case

assumptions related to the type of water body associated with railway tracks, the characteristics of the

railway track and its associated water body and the application methods used. The methodologies

have been incorporated into a modified version of the HardSPEC model, version 1.3.4, which

calculates surface water PEC‟s that are likely to result from use of herbicides applied to railway

tracks.

However, there are significant uncertainties related to the amount of track that actually receives

herbicide and the amount of attenuation that is likely to occur during run-off or leaching in any

unsaturated zone below the railway formation. Absolute worst-case assumptions of 100% of the track

target area receiving spray application and no attenuation of herbicide loads during run-off or

unsaturated zone leaching are used to calculate PECsw. Simulations based on such assumptions

should be considered as first-tier exposure assessments.

These first tier absolute worst case assumptions are included as default input parameters in the

worksheet “Herb_props” and can be changed by users to less extreme values, providing such a

change is based on a justified argument. Such simulations can be considered as second tier

exposure assessments as they incorporate more realistic assumptions but retain the identified worst-

case characteristics of the railway track formation, its embankment and associated water body.

Simulated daily PECsw in the Railway ditch for six „test compounds‟ showed that, with the exception

of weakly sorbed compounds such as atrazine and diuron, peak daily aqueous phase PECs in the

railway ditch are the result of spray drift on the day of application. This contrasts with the HardSPEC

stream scenarios where only the most strongly sorbed compounds oxadiazon and glyphosate have

peak daily aqueous phase concentrations resulting from spray drift. Such a contrast emphasizes the

need for a separate railway surface water scenario which may give a favourable risk assessment in

contrast to those for the Urban and major Road scenarios and thus enable applicants to apply for a

specific use only on railways.


different for the leaching and run-off situations and in general, run-off gives slightly higher

concentration peaks than leaching. However, such differences decrease significantly with increasing

compound sorption and, for the least mobile compounds, oxadiazon and glyphosate, leaching and


39

run-off inputs are so small that daily aqueous phase concentrations depend almost entirely on residual

masses from spray drift inputs on the day of application.

Comparison of model predictions with measured data is difficult because of the limited amount of

measured data available and significant differences in the dynamics of the water bodies simulated by

the model and sampled in the field study. Nevertheless, the limited comparisons possible indicate that

when the railway scenario is adapted to match the application conditions of the field study, the

predicted peak concentrations leaching out of the railway ballast are similar to those measured in the

water sampled from ballast trenches in the field study. When the model results are modified to match

the timing of the measured peak and integrated using 3 day running average values to try to better

reflect the study conditions, they show a very similar pattern in concentrations to that measured,

although concentrations after about 42 mm accumulated rainfall appear to be under-predicted.


40

6 REFERENCES

CRANK, J. (1956). The mathematics of diffusion. New York University Press.

DEFRA (2006). Pesticides: Code of practice for using plant protection products. Defra Publications,

London. 166 pp.

HEATHER, A.I.J., HOLLIS, J.M. & SHEPHERD, A.J. (1999). Losses of six herbicides from a

disused railway formation. Final report to Hard Surfaces project Consortium. February, 1999.

30 pp.

HOLLIS, J.M., RAMWELL, C.T. AND HOLMAN, I.P. (2004). HardSPEC: A first-tier model for

estimating surface- and ground-water exposure resulting from herbicides applied to hard

surfaces. NSRI research report No. SR3766E for DEFRA project PL0531, March 2004. 79 pp +

3 Appendices.

LINDERS, J., ADRIAANSE, P., ALLEN, R., CAPRI, E., GOUY, V., HOLLIS, J., JARVIS, N.,

KLEIN, M., MAIER, W.-M., MAUND, S., RUSSELL, M., SMEETS, L., TEIXERA, J.-L.,

VIZANTINOPOULOS, S. & YON, D. (2003). Development and description of Surface Water

Scenarios to be used in the Regulation Decision of 91/414/EEC. Final report of the FOCUS

Working Group on Surface Water Scenarios.

PARKIN, C.S. & MILLER, P.C.H. (2004). Measurements of the drift potential of a spray application

system (the Radiarc nozzle) when operating to treat areas around railway lines: a summary report.

Confidential report CR/1510/04/3471 by Silsoe Research Institute. April 2004. 6 pp + 3

Appendices.

RAMWELL, C.T., BOXALL, A.B.A. & HOLLIS, J.M. (2001). Potential contamination of surface

and groundwaters following herbicide application to a railway. Soil Survey and Land Research

Centre draft report for the Environment Agency, 22 pp.

STRANGE-HANSEN, R., HOLM, P. E., JACOBSEN, O.S. & JACOBSEN, A.S. (2004). Sorption,

mineralization and mobility of N-(phosphonomethyl) glycine (glyphosate) in five different

types of gravel. Pest Manag Sci 60: 570-578.


41

APPENDIX 1

Comparison of PEC time series for the HardSPEC railway surface water scenario with those of

the Urban and Major Road scenarios.

1

0

50

100

150

200

250

300

350

0 10 20 30 40 50 60 70 80


PE

Csw

aq

ueo

us p

hase m

g l-1

Railway Ditch-leaching

Railway Ditch-runoff

Urban stream

Major road stream


2

Figure A-1 Daily PECsw for atrazine in the Railway ditch, urban stream and major road stream.


3

0

50

100

150

200

250

300

0 10 20 30 40 50 60 70 80


PE

Csw

aq

ueo

us p

hase m

g l-1



Urban stream

Major road stream

Figure A-2 Daily PECsw for diuron in the Railway ditch, urban stream and major road stream.


4

0

10

20

30

40

50

60

70

80

0 10 20 30 40 50 60 70 80


PE

Csw

aq

ueo

us p

hase m

g l-1



Urban stream

Major road stream

Figure A-3 Daily PECsw for oryzalin in the Railway ditch, urban stream and major road stream.


5

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80


PE

Csw

aq

ueo

us p

hase m

g l-1



Urban stream

Major road stream

Figure A-4 Daily PECsw for oxadiazon in the Railway ditch, urban stream and major road stream.


6

0

1

2

3

4

5

6

7

8

0 10 20 30 40 50 60 70 80


PE

Csw

aq

ueo

us p

hase m

g l-1



Urban stream

Major road stream

Figure A-5 Daily PECsw for isoxaben in the Railway ditch, urban stream and major road stream.


7

0

2

4

6

8

10

12

14

16

18

0 10 20 30 40 50 60 70 80


PE

Csw

aq

ueo

us p

hase m

g l-1


Urban stream

Major road stream


Figure A-6 Daily PECsw for glyphosate in the Railway ditch, urban stream and major road stream.

development of a surface water exposure module for the ... of herbicide loads during run-off or...

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