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: COMPARING EMISSIONS FROM SIMULATED 18 INCH AND 24 INCHSHANK INJECTION TREATMENTS OF 1,3-DICHLOROPROPENE
Introduction
Reducing acute exposure to 1,3-dichloropropene (1,3-D) may be accomplished by three primarymeans: increased buffer zone distances, reduced use through lower application rates or acreage,
or application method changes that lead to decreased emission fluxes. The last of these options—decreased emission fluxes—is most readily achieved through use of totally impermeable films,
but the use of such films may not be not viable for certain use conditions, including orchard
fumigations. Therefore, there is a need to determine whether sufficient reductions in emission
flux can be achieved by other approaches, such as increased soil moisture or increased injection
depth. This document evaluates the potential of increased injection depth to reduce emission
fluxes.
Emissions have been long understood to decrease with application depth. A deeper injection
point essentially permits a greater proportion of injected fumigant to be sorbed and degraded in
the soil column, thereby reducing emissions. Johnson (2013) describes the prior assumption in
the department of a linear relationship between injection depth and emissions, which wasreasonably borne out by field studies. More recent developments in emissions modeling with
HYDRUS (i.e., Kandelous 2019, Brown et al. 2019, Spurlock et al. 2013) show that the model
can provide flux estimates similar to those provided by field studies, and can therefore be usefulfor prediction of flux from a variety of application scenarios. The HYDRUS model takes into
account variation in soil conditions and can thereby provide a more nuanced estimation of therelationship between injection depth and emission flux as compared to a linear approach.
In this memo, I describe simulation results for an untarped 24” deep broadcast shank injection(tentatively coined Field Fumigation Method [FFM] 1212). The simulations are performed
across 16 soil types based on measured soil properties obtained from prepared fields prior tofumigation. The results are then compared to prior simulation output for an untarped 18” deep
broadcast shank injection—currently the standard fumigation approach in much of the Central
1001 I Street • P.O. Box 4015 • Sacramento, California 95812-4015 • www.cdpr.ca.gov
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Edgar Vidrio
September 11, 2019
Page 2Valley—in order to quantify the relative emissions reduction of the 24” application. The results
are additionally evaluated on a soil-by-soil basis to understand the interaction between soil
conditions and application depth.
Methods
The methods used are essentially identical to those described in Brown (2019) and Brown et al.
(2019). In brief, HYDRUS 2D was used to simulate a shank injection application across a seriesof 16 soil types collected by DPR staff from prepared fields within 24 h prior to fumigation. I
based the layout of the untarped 24” deep broadcast scenario off the pre-existing layout for FFM
1206 (untarped 18” deep broadcast). An initial plug of fumigant was centered at 24” below thesoil surface, rather than 18”. Other aspects of the simulation domain, including materialdistribution and initial temperature distribution, were unchanged. Fumigant physicochemical
properties are the same as those described in Brown (2019).
Results
Results from the 24” simulation are summarized in Table 1. Results from the 18” simulation,
performed as part of Brown (2019), are summarized in Table 2 for convenience. Table 3
summarizes the relative decline in emissions when opting for a 24” injection in place of an 18”
injection. On average, the simulations predict a 39% decline in cumulative emissions, a 53%
decline in peak 72-hour emissions, and a 59% decline in both 24-hour and 3-hour emissions.
Figure 1 compares flux time series of 18” and 24” injection depths for each soil type andindicates a delay in the timing of peak flux under some soil conditions.
While both cumulative and peak emissions declined with increased injection depth, the extent ofreduction varied with soil type, and soil moisture conditions especially. When increasing
injection depth from 18” to 24” (45 cm to 61 cm), the additional 6” of depth occurs in thedeepest—and generally wettest—of the 3 material layers used in our HYDRUS simulations (010 cm, 10-30 cm, and 30-120 cm depths). The deepest soil layer resultantly comprises a greater
proportion of the distance between the injection point and the soil surface at the 24” injection
depth as compared to the 18” injection depth (50% vs. 33%, respectively), effectively increasing
the average soil moisture above the injection point. Therefore, the decline in emissions is due toboth increased depth and higher effective soil moisture.
Figure 2 summarizes the relationship between decline in emissions and volumetric soil watercontent of each soil, averaged between 0-24” depth, indicating a strong correlation between
average soil moisture and the relative percent reduction in emissions. At the extremes, the soilwith greatest moisture (soil # 12) saw an 80% decline in cumulative emissions with the move toa 24” depth, whereas the driest soil (soil # 5) saw just a 15% decrease. Similarly, ER declined
greatly for soils with relatively low ER under FFM 1206 (e.g., ER for soil 12 declined from 0.20

Edgar Vidrio
September 11, 2019
Page 3

to 0.04—an extremely low value), whereas ER declined only modestly for soils with high ER
under FFM 1206 (e.g., ER for soil 5 declined from 0.63 to 0.54—still very high).
Table 1. Results of simulated 24” shank injection including proportion of initial fumigantemitted (emission ratio, ‘ER’), peak 3 hour flux, peak 24 h flux, and peak 72 h flux. Soilconditions are based on field-measured values. Fluxes are based on a 100 lb/ac application rate.
Soil no.

ER

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Mean (SD)

0.15
0.08
0.08
0.35
0.54
0.43
0.24
0.34
0.44
0.16
0.31
0.04
0.26
0.13
0.22
0.26
0.25 (0.14)

Peak 3h

Peak 24h

Peak 72h

3.55
1.60
1.55
11.42
24.29
16.92
6.60
11.55
18.91
3.65
10.26
0.59
7.77
2.60
6.097.45
8.43 (6.84)

2.67
1.18
1.16
9.26
18.76
13.37
5.01
8.89
13.93
2.83
7.79
0.45
6.04
1.98
4.59
5.76
6.48 (5.27)

2.54
1.15
1.12
7.87
13.83
10.68
4.59
7.61
10.87
2.68
6.77
0.44
5.42
1.90
4.23
5.19
5.43 (3.94)(ug m-2 s-1)

(ug m-2 s-1)

(ug m-2 s-1)

Table 2. Results of simulated 18” shank injection. Soil conditions are based on field-measured
values. See Brown (2019) for additional details.
Soil no.

ER123
45

0.29
0.22
0.20
0.480.63

Peak 3h

Peak 24h

Peak 72h

9.50
5.85
5.41
25.21
37.71

7.09
4.16
3.93
19.56
32.59

6.30
3.91
3.68
14.01
19.86

(ug m-2 s-1)

(ug m-2 s-1)

(ug m-2 s-1)

Edgar Vidrio
September 11, 2019
Page 4

Soil no.

ER

678
9
10
11
12
13
1415
16
Mean (SD)

0.54
0.38
0.47
0.54
0.31
0.43
0.20
0.42
0.28
0.38
0.38
0.38 (0.13)

Peak 3h

Peak 24h

Peak 72h

31.99
14.62
25.09
32.61
10.21
20.60
4.98
19.79
7.97
14.97
16.03
17.66 (10.46)

24.54
11.60
18.3124.14
7.71
15.37
3.75
14.77
6.25
11.92
12.36
13.63 (8.46)

16.47
9.62
13.43
16.26
6.79
11.87
3.53
11.51
5.70
9.81
9.97
10.17 (4.99)(ug m-2 s-1)

(ug m-2 s-1)

(ug m-2 s-1)

Table 3. Relative decline in emissions of 24” deep injection vs. 18” deep injection
Soil no.
1
234567891011
1213141516
Mean (SD)ER-46%
-61%
-60%
-28%
-15%
-20%
-37%
-27%
-18%
-47%
-27%
-80%
-37%
-54%
-41%
-33%
-39% (18%)

Peak 3h-63%-73%-71%-55%
-36%
-47%
-55%
-54%
-42%
-64%
-50%
-88%
-61%
-67%
-59%
-54%
-59% (13%)

Peak 24h
-62%
-72%
-71%
-53%
-42%
-46%
-57%
-51%
-42%
-63%
-49%
-88%
-59%
-68%
-61%
-53%
-59% (12%)

Peak 72h
-60%
-71%
-70%
-44%
-30%
-35%
-52%
-43%
-33%
-60%
-43%
-88%
-53%
-67%
-57%
-48%
-53% (16%)

Edgar Vidrio
September 11, 2019
Page 5Figure 1. Comparison of simulated hourly flux from 24” deep (blue) and 18” deep (red)untarped broadcast shank injection presented over a 7 day period. A deeper injection reduces
peak flux and sometimes delays the timing of peak flux relative to the 18” injection.

Edgar Vidrio
September 11, 2019
Page 6

Figure 2. A strong correlation is observed between average volumetric soil water content in the
top 24” of soil and the relative reduction in emissions when changing from 18” to 24” deepshank injection. Each point is labeled with its soil number (see tables 1-3). The observationsuggests that an increase in injection depth is most effective at higher soil water contents.
DiscussionThe work here describes HYDRUS predictions of emissions from a method for which little highquality field data is available, and the few examples of sub-18” injection emissions data in theliterature provide conflicting results regarding the effectiveness of deeper applications. One suchcase describes the design and performance of a specialized shank which simultaneously injects
fumigant at 18” and 24” depths, while multiple ‘wings’ welded to the shank body are purposed
to close the shank trace and slow the upward movement of fumigant (McKenry et al. 2003, Gaoet al. 2009). Such a design would be expected to reduce emissions relative to a standard 18”
depth injection due both to the shank trace closure and the lower point of injection, but emissions
data repeatedly indicated a slight increase in emissions from the method (Gao et al. 2009). Qin etal. (2008) speculates that the lack of reduction may be attributed to systematic undersampling of
low-emission regions of the treatment rows due to the flux chambers being too narrow to fully
span the width of the treatment rows (which were ~20% wider than the control rows), or
alternatively a design issue inherent to the shank itself. Another factor contributing to the lack ofEdgar Vidrio
September 11, 2019
Page 7emissions reduction may have been the dry soil conditions of the study, reported to be between
5.1-6.6% by volume in the top meter of soil (Qin et al. 2008), which would fall near the low endof soil moisture observed as part of the DPR soil variability study (Figure 2).
Gao et al. (2018) reports 1,3-D emissions estimates from 18” and 25.5” shank injection
treatments in an orchard replant scenario. Flux time series graphs show emission reductions in
the range of 30-60% following use of a 25.5” injection as compared to a 18” injection—
consistent with the estimates of the HYDRUS modeling here—but the reliance of the study on
passive sampling chambers means that these are very rough approximations. Heavy rains andhigh reported soil moisture conditions may have also led to a greater reduction in cumulativeemissions than would normally be expected (following from the observations in Figure 2).
HYDRUS simulations and field data together suggest that a move to a 24” injection depth bepaired with an increase to the minimum allowable soil moisture. A 24” deep injection method
will most likely be used in the pre-plant fumigation of orchards and other deep-rooted perennial
crops. Experience among DPR staff suggests that fields with a history of deep-rooted crops, suchas orchards, may be particularly dry down to depths of 3-4 ft. Growers have little incentive toraise field soil moisture above current label minimums due to the expense of irrigation andbecause it is understood to reduce fumigant efficacy. However, figure 2 suggests that a 24”
injection method will provide relatively little benefit over an 18” injection (in terms of emissions
reduction) unless the field is sufficiently irrigated prior to fumigation.
A report by Kandelous and Brown (2019) describes a HYDRUS method to estimate the ‘field
capacity’ of soils sampled as part of CDPR’s soil variability study. Using these methods,
exploratory simulations suggest that a minimum moisture requirement of 50% of field capacity
would be sufficient to mitigate average cumulative emissions to those similar to those in Table 1,
but with a substantially lower ceiling of emissions (Table A1). A decrease to 40% field capacity
conditions (Table A2) yields emission estimates much higher than the averages in Table 1 andwould not be appropriate. Therefore, a minimum soil moisture content of 50% in the region
above a 24” shank injection would be appropriate in ensuring the effectiveness of the deeper
injection while greatly reducing the ceiling of potential high emissions.
Conclusions
A move towards 24” injection depth could lead to substantial 1,3-D emission reductions. On
average, the simulations predict a 39% decline in cumulative emissions and a greater than 50%
decline in several measures of peak emissions. The effectiveness of the approach relies heavily
on there being sufficient soil moisture in the region above the injection point to slow the upward
movement of fumigant through the soil profile; without the presence of such moisture, reductions
in cumulative emission are estimated to be as little as 15%. Importantly, the largest emission
reductions are observed in moist soils that already emit relatively little at shallower injection

Edgar Vidrio
September 11, 2019
Page 8points, while the drier and more problematic ‘high-emitting’ soils see only marginal reduction
with the increased injection depth. Due to the potential for this method to be primarily used insoil conditions near the lower limit of existing soil moisture requirements, it is stronglyrecommended that this method be paired with increased minimum soil moisture requirements in
the region above the injection point for effective mitigation. A minimum soil moisture of 50% offield capacity is suggested as one way to achieve similar mean cumulative emissions while
greatly improving the predictability of emissions under the proposed method.
References
Brown, C., Kandelous, M., Sartori, F., Collins, C., & Spurlock, F. (2019). Modeling variation in
1, 3-dichloropropene emissions due to soil conditions and applicator practices. Science of theTotal Environment 678. https://doi.org/10.1016/j.scitotenv.2019.04.414
Brown, C. (2019). HYDRUS-simulated flux estimates of 1,3-dichloropropene maximum periodaveraged flux and emission ratio for approved application methods. California Department ofPesticide Regulation, Sacramento, CA.
Gao, S., Hanson, B., & Qin, R. (2009). Measurement and assessment of field emission
reductions. In Proc Ann Int Res Conf on MeBr Alternatives and Emission Reductions (p. 9).
Gao, S., Doll, D. A., Stanghellini, M. S., Westerdahl, B. B., Wang, D., & Hanson, B. D. (2018).
Deep injection and the potential of biochar to reduce fumigant emissions and effects onnematode control. Journal of environmental management, 223, 469-477.
Johnson, B. (2013). Calculation of use adjustment factors for 1,3-dichloropropene with the use of
totally impermeable film for broadcast shank applications. Memorandum from Bruce Johnson toRandy Segawa dated April 26, 2013. California Department of Pesticide Regulation,
Sacramento, CA. Available at: https://www.cdpr.ca.gov/docs/emon/pubs/ehapreps/analysis_memos/2444_dichlor_film_application.pdf
Kandelous, M. (2018). A comparison between field-estimated and HYDRUS-simulated emissionof 1,3-dichloropropene from agricultural fields. California Department of Pesticide Regulation,
Sacramento, CA.
McKenry, M. V., Buessing, D., & Williams, K. (2003). New chisel shanks enable improved
fumigation of finer-textured soils. In Proc Ann Int Res Conf on Methyl Bromide Alternatives andEmissions Reductions. San Diego, CA, Oct (pp. 36-1). Available at: https://mbao.org/static/
docs/confs/2003-sandiego/papers/036%20mckenrymnewchiselshanksmbao8-29-03.pdf

Edgar Vidrio
September 11, 2019
Page 9Qin, R., Gao, S., Hanson, B., Wang, D., & Gerik, J. (2008). Shank designs and soil surface
treatments on 1, 3-D emissions in a nursery field trial. MBAO Proceedings, 31. https://mbao.org/
static/docs/confs/2008-orlando/papers/031Qin22008MBAOSummaryKearneyTria.pdf
Spurlock, F., Johnson, B., Tuli, A., Gao, S., Tao, J., Sartori, F., Qin, R., Sullivan, D.,
Stanghellini, M., Ajwa, H. (2013). Simulation of fumigant transport and volatilization fromtarped broadcast applications. Vadose Zone Journal 12. https://doi.org/10.2136/vzj2013.03.0056

Appendix
Table A1. Results of simulated 24” shank injection including proportion of initial fumigant
emitted (emission ratio, ‘ER’), peak 3 hour flux, peak 24 h flux, and peak 72 h flux. Soil
moisture conditions are fixed at 50% of field capacity. Fluxes are based on a 100 lb/ac
application rate.
Soil no.

ER

12
34
56
78
910
11121314
1516
Mean (SD)

0.26
0.24
0.22
0.22
0.19
0.20
0.31
0.23
0.27
0.21
0.29
0.21
0.25
0.22
0.25
0.26
0.24 (0.03)

Peak 3h

Peak 24h

Peak 72h

7.65
6.74
6.31
6.01
4.72
5.54
10.88
6.14
7.83
5.57
9.08
5.66
7.09
5.85
7.12
7.44
6.85 (1.53)

5.90
5.08
4.72
4.57
3.52
4.08
7.99
4.68
6.10
4.27
6.78
4.22
5.54
4.44
5.40
5.73
5.19 (1.14)

5.29
4.63
4.33
4.20
3.29
3.76
6.93
4.30
5.48
3.95
6.00
3.89
5.00
4.10
4.90
5.16
4.70 (0.93)(ug m-2 s-1)

(ug m-2 s-1)

(ug m-2 s-1)

Edgar Vidrio
September 11, 2019
Page 10

Table A2. Results of simulated 24” shank injection including proportion of initial fumigant
emitted (emission ratio, ‘ER’), peak 3 hour flux, peak 24 h flux, and peak 72 h flux. Soilmoisture conditions are fixed at 40% of field capacity. Fluxes are based on a 100 lb/ac
application rate.
Soil no.

ER12
3
4
5
67
8
9101112131415
16
Mean (SD)

0.34
0.32
0.31
0.31
0.28
0.29
0.40
0.32
0.36
0.30
0.37
0.30
0.34
0.31
0.33
0.35
0.33 (0.03)

Peak 3h

Peak 24h

Peak 72h

12.09
11.01
10.52
10.34
8.36
9.52
14.47
10.25
12.00
9.32
13.14
9.94
11.75
9.78
11.54
12.07
11.00 (1.56)

9.20
8.21
7.82
7.81
6.26
6.99
11.67
7.80
9.46
7.15
10.19
7.37
8.99
7.42
8.66
9.46
8.40 (1.38)

7.82
7.09
6.78
6.78
5.60
6.15
9.51
6.78
8.02
6.29
8.53
6.44
7.65
6.49
7.41
8.00
7.21 (1.00)(ug m-2 s-1)

(ug m-2 s-1)

(ug m-2 s-1)