Department of Pesticide Regulation
Val Dolcini
Acting Director

MEMORANDUM

TO:Edgar Vidrio
Environmental Program Manager II
Environmental Monitoring Branch

FROM:Colin Brown
Senior Environmental Scientist (Specialist)
Environmental Monitoring Branch916-445-9579

DATE:

September 11, 2019

Gavin NewsomGovernor
Jared Blumenfeld
Secretary for
Environmental Protection

Original Signed By

SUBJECT: SIMULATION OF 1,3-DICHLOROPROPENE EMISSIONS FROM A
BROADCAST APPLICATION WITH PARTIAL LOW PERMEABILITY FILM
SURFACE COVER

Field fumigation methods (FFMs) are regulatory prescriptions of field management practices forthe application of a fumigant, each of which is given a unique code (‘FFM Codes’, see CDPR
2017). For applications of 1,3-dichloropropene (1,3-D), the selection of an FFM by an applicator
has implications for both buffer zone credits and the emissions weighting used under thetownship cap system (CDPR 2016). The FFMs available to an applicator may also vary withseason (CDPR 2016), regional air quality concerns (3 CCR § 6448.1[d]), or a field’s history offumigation (3 CCR § 6448.1[c]). While an applicator may choose to go beyond the minimum
requirements of an FFM, there is little incentive for this extra expense because no additionalemission or buffer zone credits are given. Therefore, where the use of a new method isencouraged, it is ideally introduced as a new FFM and accompanied by its own emission
estimates and buffer zone credits, if applicable.
This document describes HYDRUS simulation of a proposed application method (designatedhere as 'FFM 1250') that combines elements of ‘totally impermeable film’ (TIF) strip
applications (FFM 1249) and untarped deep broadcast applications (FFM 1206). Such a method
is being evaluated for potential use as an application method in orchard fumigations to determine
if this method would satisfactorily mitigate emissions while reducing the high costs associatedwith broadcast TIF methods. Under the proposed application method, a field is fumigated aswould be done in a broadcast application at a 45-cm (18”) injection depth (all rows receivingfumigant), but with only alternate rows sealed with TIF. This differs from the existing TIF strip
method in that both tarped and untarped rows are fumigated, rather than only tarped rows.
Methods
The simulation methods used here are essentially identical to those described by Brown (2019).
In brief, HYDRUS 2D was used to simulate a modified TIF strip injection application across a
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Edgar Vidrio
September 11, 2019
Page 2

series of 16 soil types collected by DPR staff from prepared fields within 24 h prior tofumigation (see Brown 2019 for a description of soil properties). Simulation results are output at
1-h intervals over 21 days, from which estimates of cumulative flux and period-averaged peakemissions can then be estimated.
In designing the simulation of the proposed method, I referenced Spurlock (2014), who describes
the original simulation design of the strip configuration. He describes strip applications ascommonly using 5 to 7 shanks at 51-61 cm spacing (20”-24”) with a typical row width of 335 cm(11’), each row being covered with a 396 cm (13’) wide tarp, and each end being tucked
approximately 30 cm (12”) into the soil. Untreated rows of various widths (depending on orchardtype) are then left between treated strips. Spurlock (2014) assumed a narrower untreated row
width relative to treated row width, such that the area covered by TIF amounted to approximately
70% of the domain area (when considering the tarp ‘tuck’).
The present simulations relied on the original TIF strip domain design as a template;modifications were then implemented to meet the design requirements. These modifications
consisted of (1) the insertion of additional solute injection points in the untarped row and (2) thewidening of the untarped row to match the width of the tarped row. The widening of the untarped
row width was considered necessary as—with the addition of fumigant—the width of theuntarped row is now constrained by rig shank spacing. Like the original TIF strip application
method, fumigation plugs were spaced evenly at 51 cm intervals (center-to-center) and centeredat 45 cm depth across the entirety of the modeling domain (Figure 1). Separate simulations wereperformed with simulated tarp-cuts at 9 days (the current minimum) and 14 days.

Figure 1. Schematic of the domain geometry used in simulations of the proposed ‘Broadcast TIF Strip’ application
method. Fumigant plugs (red) are centered 45 cm below surface level and spaced at 51 cm intervals. A surface seal of TIF(blue) is tucked into the soil at the edges and covers approximately half of the domain width.

A separate series of simulations was performed to test the effect of row width on emissions while
maintaining the ratio of tarped to untarped surface area (approximately 50:50). These simulations

Edgar Vidrio
September 11, 2019
Page 3

used a shortened domain length of 251 cm. The primary simulations (as shown in Figure 1)
assume a tarp width of approximately 13 feet (392 cm), which is the standard roll width forbroadcast tarp. The narrow domain assumes a tarp width of 9.8’ (118 cm), a non-standard width
which is only evaluated for purposes of understanding the implications of row spacing. In
practice, it is unlikely that anything other than a 13-foot width would be applied in a strip
application due to this being the only standard (i.e., non-custom) size for broadcast and strip
applications, and the increased material and labor costs associated with narrower bed-specifictarps (H. Ajwa, personal communication).
Results
Results from the simulations are summarized in Tables 1 and 2. Orchard applications arepresently performed as either untarped, deep shank injections (FFM 1206) or as TIF strip
applications (FFM 1249). The proposed TIF strip broadcast method yields emissions lower thanthose of FFM 1206 but higher than those of FFM 1249. Table 3 summarizes emission values foreach of these three orchard methods, and a comparison of flux profiles with these methods isshown in Figure 2.
Unlike broadcast TIF methods, an extended holding period of 14 days had minimal effect on
cumulative emissions, and no effect on peak emission values. Emission profiles (Figure 2)
suggest that this is likely due to preferential transport through the untarped area of the soil
surface prior to tarp-cut, resulting in peak flux values occurring in the first few days following
application and resulting in a minimal ‘flush’ of fumigant emission at tarp-cut that would
otherwise be mitigated with an extended holding time.
Negligible differences in peak and cumulative flux were observed on the basis of change in row
spacing, under the condition of constant ratio between tarped and untarped area (Table A2).
Should applicators vary the ratio of tarped-to-untarped row area, important differences inemissions will occur, with emission values approaching those of FFM 1206 (ER = 0.38) as theproportion of untarped area increases. It is an assumption of this analysis that such changes inproportion are unlikely to be common due to the need to adjust shank spacing with each pass,although it possible to envision edge cases where an applicator may fumigate two untarped rows
for every tarped row. For this reason, it is recommended that the definition for FFM 1250 require(1) at least one tarped row for every one untarped row, (2) constant row width, and (3) a constant
application rate between rows.
As observed in prior simulations, substantial variation in emissions is possible due to variation insoil conditions, specifically soil moisture. Use of a higher moisture minimum would be one
method to reduce the potential for higher-than-expected emissions from the proposed method
resulting from very dry soil. Using methods described by Kandelous and Brown (2019), a
minimum moisture requirement of 50% of field capacity would be sufficient to mitigate averageEdgar Vidrio
September 11, 2019
Page 4

cumulative emissions to those similar to those in Tables 1 and 2, but with a substantially lower
ceiling of emissions (Table A1).
Table 1. Summary of HYDRUS output for the simulated ‘Broadcast TIF Strip’ method with a 9 day holding period prior
to tarpcut. Per CDPR convention, emission values have been normalized to a 100 lb/ac application rate.

Soil no.

ER1
23456789101112131415
16
Mean (SD)

0.20
0.15
0.14
0.33
0.48
0.39
0.26
0.32
0.36
0.21
0.31
0.15
0.28
0.20
0.26
0.26
0.27 (0.09)

Peak 3h

Peak 24h

Peak 72h(ug m-2 s-1)

(ug m-2 s-1)

(ug m-2 s-1)

5.56
3.66
3.29
13.16
21.72
18.12
8.62
12.97
18.36
5.44
12.05
3.01
9.23
5.11
8.15
8.43
9.80 (5.79)

4.15
2.54
2.40
9.66
17.72
13.34
6.55
9.45
12.34
4.13
8.66
2.04
7.02
3.70
5.90
6.39
7.25 (4.42)

3.82
2.39
2.25
7.71
11.67
9.63
5.64
7.57
9.03
3.82
7.10
1.97
6.06
3.43
5.22
5.52
5.80 (2.84)

Table 2. Summary of HYDRUS output for the simulated ‘Broadcast TIF Strip’ method with a 14 day holding periodprior to tarpcut. Emission values are virtually unchanged by the longer holding period, likely due to rapid loss offumigant from the untarped area prior to tarpcut. Per CDPR convention, emission values have been normalized to a 100lb/ac application rate.

Edgar Vidrio
September 11, 2019
Page 5

Soil no.

ER12
34
5678
910
11
12
13
14
1516
Mean (SD)

0.19
0.14
0.13
0.31
0.45
0.36
0.25
0.30
0.34
0.19
0.29
0.13
0.26
0.19
0.24
0.24
0.25 (0.09)

Peak 3h

Peak 24h

Peak 72h(ug m-2 s-1)

(ug m-2 s-1)

(ug m-2 s-1)

5.56
3.66
3.29
13.16
21.72
18.12
8.62
12.97
18.36
5.44
12.05
2.92
9.23
5.11
8.15
8.43
9.80 (5.79)

4.15
2.54
2.40
9.66
17.72
13.34
6.55
9.45
12.34
4.13
8.66
2.04
7.02
3.70
5.90
6.39
7.25 (4.42)

3.82
2.39
2.25
7.71
11.67
9.63
5.64
7.57
9.03
3.82
7.10
1.97
6.06
3.43
5.22
5.52
5.80 (2.84)

Table 3. Mean cumulative emission and peak flux values for three common orchard fumigation methods: FFM 1206
(untarped, 18” injection), FFM 1249 (TIF strip 18” injection), and the proposed method, tentatively FFM 1250 (TIF strip
broadcast 18” injection). Emissions for FFM 1250 are predicted to be slightly higher than the mean of FFM 1206 andFFM 1249.

FFM

ER12061249
1250

0.38 (0.13)
0.13 (0.07)
0.27 (0.09)

Peak 3h

Peak 24h

Peak 72h(ug m-2 s-1)

(ug m-2 s-1)

(ug m-2 s-1)

17.66 (10.46)
8.08 (3.68)
9.80 (5.79)

13.63 (8.46)
3.11 (1.29)
7.25 (4.42)

10.17 (4.99)
2.06 (1.05)
5.80 (2.84)

References
Brown, C. (2019). HYDRUS-simulated flux estimates of 1,3-dichloropropene maximum periodaveraged flux and emission ratio for approved application methods. California Department of
Pesticide Regulation, Sacramento, CA.

Edgar Vidrio
September 11, 2019
Page 6

California Code of Regulations, Title 3, Section 6448.1 (2019). 1,3-Dichloropropene field
fumigation methods. California Code of Regulations (Title 3. Food and Agriculture), Division 6.
Pesticides and Pest Control Operations. https://www.cdpr.ca.gov/docs/legbills/calcode/020404.htm
CDPR (2017). Appendix J – 1,3-dichloropropene (field fumigant) recommended permit
conditions. Pesticide use enforcement program standards compendium, vol.3, restricted materialsand permitting. California Department of Pesticide Regulation, Sacramento, CA.
https://www.cdpr.ca.gov/docs/enforce/compend/vol_3/rstrct_mat.htm
CDPR (2016). Risk management directive and mitigation guidance for cancer risk from 1,3dichlorpropene [sic] (1,3-D). Memorandum from Teresa Marks to Marylou Verder-Carlos andGeorge Farnsworth dated October 6, 2016. California Department of Pesticide Regulation,Sacramento, CA. https://www.cdpr.ca.gov/docs/whs/pdf/1,3-d_directive_mitigation.pdf
Kandelous, M. and Brown, C. (2019). Effect of pre-application soil moisture on 1,3-D emissions.
Draft memorandum from Maziar Kandelous and Colin Brown to Edgar Vidrio dated July 15,
2019. California Department of Pesticide Regulation, Sacramento, CA.
Spurlock, F. (2014). HYDRUS estimates of cumulative 1,3-dichloropropene and chloropicrin
emissions from low permeability tarp strip applications. California Department of Pesticide
Regulation, Sacramento, CA. https://www.cdpr.ca.gov/docs/emon/pubs/ehapreps/analysis_
memos/2494_hydrus_estimates.pdf

Edgar Vidrio
September 11, 2019
Page 7

Figure 2. Time series of predicted 1,3-D flux for each set of soil conditions for FFM 1206 (red dashes), FFM 1249 (bluedots), and FFM 1250 (solid black). Flux profiles are based on a 9 day tarp holding period for FFM 1249 and 1250. See
Brown (2019) for a description of each soil type.

Edgar Vidrio
September 11, 2019
Page 8

Table A2. Summary of HYDRUS output for the simulated ‘Broadcast TIF Strip’ method with a 9 day holding periodprior to tarpcut. The simulation uses simulated moisture conditions of 50% of field capacity, rather than moisture
conditions based on measured field values as part of the CDPR soil variability study. Per CDPR convention, emission
values have been normalized to a 100 lb/ac application rate.

Soil no.

ER1
2
3
4
5
6
7
8
910
1112
13
141516Mean (SD)

0.32
0.30
0.29
0.28
0.25
0.27
0.35
0.29
0.32
0.28
0.34
0.270.30
0.28
0.30
0.31
0.25 (0.02)

Peak 3h

Peak 24h

Peak 72h(ug m-2 s-1)

(ug m-2 s-1)

(ug m-2 s-1)

8.96
8.25
7.78
7.06
6.37
7.21
11.62
7.47
8.71
7.16
10.39
6.68
8.28
7.24
8.15
8.35
8.11 (1.36)

7.12
6.27
5.81
5.21
4.52
5.17
8.43
5.59
6.86
5.17
7.71
4.80
6.19
5.41
6.05
6.33
6.04 (1.07)

5.86
5.32
5.01
4.61
4.12
4.55
6.81
4.90
5.81
4.60
6.40
4.33
5.33
4.75
5.25
5.45
5.19 (0.75)

Edgar Vidrio
September 11, 2019
Page 9Table A2. Summary of HYDRUS output for the simulated ‘Broadcast TIF Strip’ method with a 9 day holding period andnarrow row spacing. The ratio of tarped-to-untarped area matched that of other FFM 1250 simulations. The resulting
values are nearly identical to those described in Table 1. The results suggest that row spacing is unimportant provided
that the ratio of tarped-to-untarped area is held constant.

Soil no.

ER1
2
3
45678910111213
1415
16
Mean (SD)

0.20
0.15
0.14
0.33
0.49
0.390.26
0.32
0.37
0.21
0.31
0.15
0.28
0.20
0.26
0.26
0.27 (0.10)

Peak 3h

Peak 24h

Peak 72h(ug m-2 s-1)

(ug m-2 s-1)

(ug m-2 s-1)

5.52
3.58
3.33
13.05
21.76
18.07
8.56
12.89
18.38
5.41
11.93
2.94
9.19
5.04
8.06
8.40
9.76 (5.80)

4.13
2.49
2.30
9.59
17.70
13.29
6.50
9.41
12.29
4.11
8.61
2.00
6.96
3.65
5.83
6.36
7.20 (4.43)

3.76
2.33
2.19
7.69
11.72
9.64
5.60
7.57
9.04
3.77
7.08
1.93
6.02
3.39
5.18
5.49
5.78 (2.87)