BEFORE THE DIRECTOR OF THE 

DEPARTMENT OF PESTICIDE REGULATION 

STATE OF CALIFORNIA 

In the Matter of the Responsible Farmers Coalition’s 

Request for Approval of 

Reduced Volatile Organic Compound 

Emissions Field Fumigation Methods 

DECISION

(California Code of Regulations, Title 3, section 6452) 

RESPONSIBLE FARMERS COALITION 

Mr. John Guerard 

c/o Bolthouse Farms 

7200 East Brundage Road 

Bakersfield, California 93307 

______________________________/ 

Summary 

The Responsible Farmers Coalition submitted a study to the Department of Pesticide 

Regulation (DPR) titled “Field Volatility of MITC After Application of Metam-Sodium by 

Chemigation and Shank Injection Comparing Standard Water Sealing and Pulsed Water Sealing” 

dated October 18, 2007. As part of DPR’s efforts to reduce volatile organic compound (VOC) 

emissions, most night applications of methyl isothiocyanate (MITC)-containing pesticides are 

prohibited within several ozone nonattainment areas (NAAs) during May–October, under Title 3, 

California Code of Regulations (3 CCR) section 6450.1(c). However, the regulations also 

include a provision for the DPR Director to grant interim approval of fumigation methods that 

reduce VOC emissions (3 CCR section 6452). DPR has completed its evaluation of the two 

fumigation methods described in the study as specified in 3 CCR section 6452. The submitted 

study indicates high uncertainty as to exact emissions for the two methods. Despite the 

uncertainty of the data, DPR has determined that the methods meet the ultimate test for approval 

as interim methods, as described below. Effective May 1, 2008, DPR grants approval for interim 

use of the shallow shank injection method described in the study in all five ozone NAAs. 

Effective May 1, 2008, DPR grants approval for interim use of the sprinkler method described in 

the study for the Sacramento Metro and South Coast ozone NAAs, but not the San Joaquin 

Valley, Southeast Desert, or Ventura ozone NAAs during May–October. The emission ratings 

assigned to these methods will be equal to the highest rating for any currently approved method 

for metam-sodium in each specific area. The methods described in the study may be used for 

three years from the effective date, contingent on the submittal of an additional study to more 

accurately document the emissions from these fumigation methods. 
Responsible Farmers Coalition 

Page 2 

Background 

VOCs contribute to the formation of ozone, a major air pollutant in several regions of California. 

Under the federal Clean Air Act, California’s State Implementation Plan for ozone includes an 

element to track and reduce VOC emissions from pesticides. On January 25, 2008, DPR adopted 

regulations to control VOC emissions from fumigants during the May–October peak ozone 

season in five ozone NAAs: Sacramento Metro, San Joaquin Valley, Southeast Desert, South 

Coast, and Ventura. 

The Responsible Farmers Coalition submitted comments for DPR’s regulations during the 

rulemaking process. During this rulemaking process, DPR modified its originally proposed text 

and provided the public an opportunity to comment on the modifications. As part of their 

comments, the Responsible Farmers Coalition included a study on field emissions from several 

experimental applications of metam-sodium at night, “Field Volatility of MITC After 

Application of Metam-Sodium by Chemigation and Shank Injection Comparing Standard Water 

Sealing and Pulsed Water Sealing” dated October 18, 2007. This study and comments on night 

applications of metam-sodium were not relevant to the modifications, and therefore, no revisions 

to the regulations were considered at that time. DPR has since adopted the regulations, including 

a provision prohibiting most night applications of MITC-containing pesticides [3 CCR 

section 6450.1(c)]. However, the regulations also include a provision for interim approval of 

fumigation methods with emissions no greater that the field fumigation methods allowed in the 

regulations in the respective areas (3 CCR section 6452). 

Regulatory Standards and Considerations 

Title 3, CCR section 6452 sets different standards by which to evaluate whether a new 

fumigation method will be allowed, one for the Sacramento Metro and South Coast ozone NAAs 

and one for the San Joaquin Valley, Southeast Desert, and Ventura ozone NAAs. Sacramento 

Metro and South Coast have a less stringent standard because no further VOC reductions from 

pesticides are needed in these ozone NAAs. Both “low-emission” and “high-emission” methods 

can be used in these two areas. Only “low-emission” methods are allowed in the San Joaquin 

Valley, Southeast Desert, and Ventura ozone NAAs during the May–October peak ozone season. 

The key information is the emission rating (percent of the fumigant applied that is emitted to the 

air) and the emission rate (emission rating multiplied by the maximum application rate). Either 

the emission rating or the emission rate can be no greater than the current methods allowed 

within the ozone NAAs by the regulations. The following table shows the standard for approval 

of an interim method for MITC, based on DPR’s current emission estimates. 
Responsible Farmers Coalition 

Page 3 

Ozone Nonattainment Area 

Maximum Allowed 

MITC Emission Rating 

(percentage) 

Maximum Allowed 

MITC Emission Rate 

(pounds/acre) 

Sacramento Metro, South Coast 77 140 

San Joaquin Valley, Southeast 

Desert, Ventura 28 51 

In assessing whether the new method meets the standard, DPR must assess the scientific data 

submitted to establish the emission rating, normally consisting of field monitoring data. In 

evaluating this data, 3 CCR section 6452 requires DPR to consider the following factors: 

• whether the information is sufficient to estimate emissions. 

• whether the results are valid as indicated by the quality control data. 

• whether the conditions studied represent agricultural fields. 

Summary and Evaluation of the Submitted Information 

The Responsible Farmers Coalition submitted the study entitled “Field Volatility of MITC 

After Application of Metam-Sodium by Chemigation and Shank Injection Comparing Standard 

Water Sealing and Pulsed Water Sealing” by Dr. David Sullivan and Dr. Husein Ajwa, dated 

October 18, 2007, to support its request to allow metam-sodium applications at night. 

Dr. Sullivan and Dr. Ajwa measured the MITC emissions for two metam-sodium fumigation 

methods: shallow injection using tractor shanks and chemigation using sprinklers. All 

applications were initiated on July 26, 2007, between 1:00 a.m. and 2:00 a.m., and completed 

between 1:45 a.m. and 6:00 a.m. In addition to the two fumigation methods, Dr. Sullivan and 

Dr. Ajwa measured emissions from “standard” water treatments (continuous water application) 

and “pulsed” water treatments (alternating periods of water and no water application). Two water 

treatments were applied for all four applications, one immediately after application and the 

second during the evening of the day of application. All four applications were approximately 

2.5 acres in size, separated by 900-1,600 feet, located in Kern County, and with metam-sodium 

applied at 75 gallons/acre (320 pounds active ingredient/acre). Using a combination of integrated 

horizontal flux and off-site back-calculation techniques, Dr. Sullivan and Dr. Ajwa estimated the 

following emissions for MITC over the four-day study period (emission rating and emission 

rate): 

• night sprinkler with two pulsed water treatments: 37.65 percent and 67 pounds/acre. 

• night sprinkler with two standard water treatments: 35.68 percent and 64 pounds/acre. 

• night shallow injection with two pulsed water treatments: 2.22 percent and 4.0 pounds/acre. 

• night shallow injection with two standard water treatments: 2.10 percent and 

3.7 pounds/acre. 
Responsible Farmers Coalition 

Page 4 

The report submitted on October 18, lacked some key information. DPR requested additional 

information in November 2007 and received it in December 2007. After several more phone 

calls and e-mail exchanges, DPR staff had a final discussion with Dr. Sullivan and Dr. Ajwa on 

February 13, 2008, and the last requested information was received on February 15, 2008. 

DPR’s scientific review of the report describes several shortcomings, both with the design and 

execution of the study. The most critical issues include: 

• uncertainty of the air concentrations due to nonlinear calibration curves for the laboratory 

instrument. 

• uncertainty of the air concentrations due to variable recoveries (28–175 percent) of samples 

containing known amounts of MITC (spiked samples). 

• sampling halted when sprinklers were running. 

• uncertainty in the emissions for some periods due to an insufficient number of valid samples 

or air concentrations that increased with height. 

Additional work by the study authors or review of additional information by DPR would not 

further resolve these issues. Even with these shortcomings, many of the results are reasonably 

consistent with the results from other studies, particularly for the sprinkler application. While not 

preferred by the scientific staff, it is possible with a reasonable amount of certainty to set an 

upper-bound for the emission rates that will not be exceeded for these application methods. The 

attached memorandum contains the detailed review. 

Findings 

The information provided, particularly the quality control data, indicates high uncertainty with 

the exact emissions for these fumigation methods. However, DPR staff is confident that the 

emissions are no greater than other fumigation methods currently in use. Therefore, DPR has 

assigned the following emission ratings to these methods: 

• MITC night shallow injection method: 28 percent (based on current shallow injection method 

with two post-fumigation water treatments). 

• MITC night sprinkler method: 77 percent (based on current sprinkler method with one 

post-fumigation water treatment). 

Conclusions 

The emission ratings and the current maximum application rate of 320 pounds per acre of 

metam-sodium and 350 pounds per acre of metam-potassium support approval of these 

fumigation methods. Effective May 1, 2008, the MITC night shallow injection method is 

approved for use in all five ozone NAAs. Effective May 1, 2008, the MITC night sprinkler 
Responsible Farmers Coalition 

Page 5 

method is approved for use in the Sacramento Metro and South Coast ozone NAAs, but not the 

San Joaquin Valley, Southeast Desert, or Ventura ozone NAAs during May–October. These 

fumigation methods may be used anytime outside of ozone NAAs and within any ozone NAA 

outside the May–October period, consistent with all VOC fumigation method restrictions. 

In addition, the fumigation method descriptions and photographs for the shallow injection 

method show significant differences from the methods currently described in the regulations. 

Growers and applicators fumigating with the night shallow injection method must follow the 

regulatory recommendations for equipment and procedures described in part VI of the attached 

memorandum. 

DPR grants interim approval of these fumigation methods for three years from the effective date. 

Due to the high uncertainty of the emission estimates, continued use of these fumigation methods 

beyond three years is contingent on the submittal of an additional acceptable study to more 

accurately document the emissions. Since DPR must adopt regulations to include these new 

methods prior to the expiration of the interim approval, the additional study should be submitted 

within 12 months. The additional study should include a comparison of the shallow injection 

method used for this study and the typical shallow injection method previously monitored (as 

described in the series of studies by D.L. Merricks in 1999, 2001, and 2002). DPR recommends 

that the Responsible Farmers Coalition submit a draft protocol for DPR scientific staff review 

prior to initiating the study. 

By: ___ for_______ Date:______2/29/08___________ 

 Mary-Ann Warmerdam, Director 

Department of Pesticide Regulation 

Attachment 
Department of Pesticide Regulation

Mary-Ann Warmerdam M E M O R A N D U M Arnold Schwarzenegger Director Governor 

TO: Randy Segawa 

 Environmental Program Manager I 

Environmental Monitoring Branch 

FROM: Pamela Wofford Original signed by 

Senior Environmental Scientist 

Environmental Monitoring Branch 

(916) 324-4297 

DATE: April 23, 2008 

SUBJECT: AMENDMENT TO REVIEW OF “FIELD VOLATILITY OF METHYL 

ISOTHIOCYANATE AFTER APPLICATION OF METAM-SODIUM BY 

CHEMIGATION AND SHANK INJECTION COMPARING STANDARD 

WATER SEALING WITH PULSED WATER SEALING”

In a memorandum to you dated February 26, 2008, Terrell Barry, Shifang Fan, and I described a 

review of a study on the emissions of methyl isothiocyanate from two metam-sodium fumigation 

methods: night shank injection with two water treatments and night sprinkler application with 

two water treatments. We mistakenly described part of the configuration of the application 

tractor used for the shank injection portion of the study. The compaction equipment was 

described as: 

“The application tool bar(s) are followed by a ring roller with four gauge wheels controlled by 

hydraulic cylinders to control depth and or pressure to seal the chisel trace that is as least as wide 

as the application tool bar. The ring roller will be followed with a coil packer that is as least as 

wide as the application tool bar.” 

The compaction equipment and recommended permit conditions should instead be described as 

“The application tool bar(s) are followed by a ring roller with four gauge wheels controlled by 

hydraulic cylinders to control depth and or pressure to seal the chisel trace that is as least as wide 

as the application tool bar, or a coil packer that is as least as wide as the application tool bar.” 

1001 I Street • P.O. Box 4015 • Sacramento, California 95812-4015 • www.cdpr.ca.gov 

A Department of the California Environmental Protection Agency 

Printed on recycled paper, 100% post-consumer--processed chlorine-free. 
Department of Pesticide Regulation

Mary-Ann Warmerdam M E M O R A N D U M Arnold Schwarzenegger Director Governor 

TO: Randy Segawa 

 Environmental Program Manager I 

Environmental Monitoring Branch 

FROM: Terrell Barry, Ph.D., Research Scientist III Original signed by 

Environmental Monitoring Branch 

Shifang Fan Ph.D., Environmental Scientist Original signed by 

Environmental Monitoring Branch 

Pamela Wofford, Senior Environmental Scientist Original signed by 

Environmental Monitoring Branch 

(916) 324-4297 

DATE: February 26, 2008 

SUBJECT: REVIEW OF “FIELD VOLATILITY OF METHYL ISOTHIOCYANATE AFTER 

APPLICATION OF METAM-SODIUM BY CHEMIGATION AND SHANK 

INJECTION COMPARING STANDARD WATER SEALING WITH PULSED 

WATER SEALING” 

I. Background 

This field study had two main objectives: (1) measure flux from night metam sodium 

applications, and (2) compare evening watering-in that is applied over a two hour period with 

pulsed watering-in applied over a four hour period (30 minutes on/30 minutes off). 

The original report did not contain enough detail to fully review the results. For example, the 

on-field mast measured air concentrations are shown in a plot but not in a table. In addition, the 

flux calculations were not included. Subsequently the authors submitted for review the quality 

assurance/quality control (QA/QC) data collected for the study and the spreadsheets and 

calculations used to estimate the flux for both methods. A review of those data is included in this 

memorandum. 

This is the first night time shank application study submitted. In addition, the application rig is 

significantly different from the typical rig used in California. The applicator has submitted 

photographs and the rig specifications to the Department of Pesticide Regulation (DPR) for 

review. Before night shank applications using this rig are allowed, a second study should be 

conducted to verify that the emissions are reliably as low as those measured in this study since 

the results are so different from previous shank application method results. The additional study 

should include both the application rig used in this study (Western Farms rig) and the typical 

application rig used in the Merricks studies (Merricks, 1999; Merricks, 2001; Merricks, 2002). 

1001 I Street • P.O. Box 4015 • Sacramento, California 95812-4015 • www.cdpr.ca.gov 

A Department of the California Environmental Protection Agency 

Printed on recycled paper, 100% post-consumer--processed chlorine-free. 
Randy Segawa 

February 26, 2008 

Page 2 

Due to considerable uncertainty in the laboratory QA/QC and irregularities in the fieldwork 

(both discussed in detail below), it should be assumed that emissions for this new rig are the 

same as the typical rig. However, the typical rig used for metam sodium applications should not 

be allowed for night applications. 

When differences in timing of the application are considered the sprinkler results are reasonably 

similar to the previous sprinkler results. The flux and concentrations are high during the night 

application. These results do not support allowing night sprinkler applications unless mass loss in 

the context of the volatile organic compound (VOC) regulations includes a large uncertainty 

factor. Acute exposure and buffer zones to protect persons off-site are not addressed in this 

review. Concentrations and flux decreases during the day and first the evening. As observed in 

previous studies, the intermittent watering-in performed early the first evening damps the 

increase in flux and air concentrations that has been observed for metam in standard watering-in 

studies. These results indicate that the total mass loss of approximately 37% for the sprinkler 

application method used in this study is less than the standard day sprinkler method (77%) but 

more than the intermittent watering-in day sprinkler application (28%). Uncertainty in the quality 

of these results infers a mass loss larger than the 37% estimated in this study. 

Detailed review of the laboratory QA/QC and the fieldwork are presented separately below. 

II. Laboratory Quality Assurance and Quality Control Comments 

This part of the review is focused on quality measures of methyl isothiocyanate (MITC) 

monitoring. During review, we had telephone, e-mail and a teleconference call exchanges with 

the University of California, Davis laboratory to obtain more detailed information concerning the 

laboratory analysis. 

QA/QC measures for field samples included 12 duplicate samples at one sampling station, 

triplicates of field blank, and triplicates of trip spikes and field spikes each of three levels. QA/QC 

measures for laboratory analysis included determination of the detection limit as 2 μg/sample and 

44 lab spike samples prepared by adding 10 μl of 10.8 μg MITC/μl of a standard fortification 

solution to the middle of the charcoal tube on the day the field samples arrived in the laboratory. 

The spiked tubes were stored, extracted and analyzed the same as the field samples. One 

laboratory spike was analyzed with every ten field samples. Based on the revised protocol for 

MITC analysis, these laboratory spikes were used “as standard QC/QA to confirm MITC storage 

stability on charcoal, extraction efficiency, and the GC measurement accuracy.” 
Randy Segawa 

February 26, 2008 

Page 3 

DPR has seven major concerns about the laboratory practices: 

1. Spiked samples at different concentrations should have been analyzed prior to the study to 

validate the gas chromatograph/mass spectrometry (GC/MS) method used for this study. 

According to e-mail communication: “the laboratory has been running MITC analyses 

following the Morse protocol using the NP detector since 2002, the GC/MS used for this 

study is a new GC purchased early last year. The laboratory used this GC because it was not 

expected that the concentrations were much lower than previous studies.” The laboratory 

spikes mentioned above could not serve as analytical method validation since all spikes were 

at one concentration level of 108 μg MITC/tube. Standard laboratory practice is three to 

seven different levels for analytical method validation studies to cover concentration ranges 

of field samples. The reported results of field samples in this study ranged from 1 to 

160 μg/tube. 

2. A trapping efficiency study should have been conducted. The field spikes might provide 

information for trapping efficiency; however they were sampled in the field for only four 

hours and the results of the field spikes were highly variable. The field samples ran from 

three to eight hours. 

3. The results of the single concentration laboratory spikes show a declining trend with analysis 

sequence (Figure 1). This indicates a systematic bias that increases over time. 

4. The field QA/QC samples showed variable results and indicate possible problems. The 

results of field blank samples ranged from 0 to 0.87 μg/tube. Positive field blanks indicate a 

contamination problem. Recoveries of several trip spikes were high, ranging from 84.4% to 

174.8%. Plus, these are inconsistent with the field spike results that showed low recoveries, 

ranging from 27.7% to 109%. 

5. The laboratory standard calibration curves used to calculate the sample results were not 

linear (R2

=0.9793) (Figure 2). For side-by-side comparison, a typical standard calibration 

curves (R2=0.9997) from the California Department of Food and Agriculture’s laboratory is 

shown in Figure 3. Using a linear model for the nonlinear calibration curve leads to incorrect 

sample concentration results, particularly at low concentrations. 

6. There is an inconsistency in MITC air concentrations between the data on page 77 of 

Sullivan Environmental Consulting, Inc.’s report and the data DPR calculated using the 

laboratory analysis results. Via e-mail communications, it turned out that the inconsistency 

was due to a subtraction of 0.6 μg/ml (6 μg/tube) from all analysis results including both 

on-field and off-field samples. This subtraction of 0.6 μg/ml was based on the average of 

differences between the results calculated by subtracting the y-intercept versus those 

calculated by forcing the slope through zero for the on-field samples. The differences of each 
Randy Segawa 

February 26, 2008 

Page 4 

paired data ranged from -4.38 to 0.96 μg/ml. The investigators made these adjustments in an 

attempt to correct the nonlinear problems of the calibration curve discussed in number 5. 

DPR does not believe that either forcing the slope through zero or subtracting 6 ug/tube is an 

appropriate adjustment for this problem. In addition, making both adjustments appears to 

double-correct the results, underestimating the true concentrations. Attempting any 

recalculation of the results at this time is problematic. 

7. One of purposes of this study was to compare MITC emission from different application 

methods, chemigation versus shank injection and standard water sealing versus pulsed water 

sealing. However, all samples of chemigation were analyzed in one period (July 31, 2007, 

15:38 to August 1, 2007, 11:03) and results were calculated using one standard curve 

(calibration slope); all samples of shank injection were analyzed in another period (August 1, 

2007, 15:44 to August 3, 2007, 3:10) and results were calculated using a different standard 

curve (calibration slope). This sample analysis schedule may introduce systematic errors that 

would confound comparison of different application methods. 

The following are specific comments on the different documents: 

On Revised Protocol: 

1. Page 1, the paragraph of Stock Solution, the last sentence: This stock solution should contain 

0.995 mg MITC /ml since the purity is 99.5%. 

2. Page 2, the first paragraph: Either the concentration unit of the spiking standard or the 

procedure was wrong. If following the procedure, the spike standard solution concentration 

should be 10 μg/ml, not 10 μg/μl. Also the purity of the MITC analytical standard should be 

considered. 

3. Page 2, the paragraph of Field Sample Fortification: If following the procedure that 10 μl of 

0.05, 1.0, and 20 μg/ml MITC standard solutions was spiked, the fortified tubes should have 

contained 0.0005, 0.01, and 0.2 μg/tube MITC, not 0.5, 10, and 200 μg/tube. It is possible 

that the concentration unit of the spiking solutions was wrong. 

On Report: 

1. Page 33, the median values were used for field spike recovery values, 95.2 to 109.2%. With 

only three samples, a range should have been reported instead of the median. 

2. Page 35, the last sentence: it is unclear how the 2 μg/tube was converted to 20 μg/m3

. With a 

flow rate of 1 liter/minute, the sampling time would be only 100 minutes. However, most 

samples ran approximately 200-500 minutes. 
Randy Segawa 

February 26, 2008 

Page 5 

3. Page 36, the analytical standard purity, date of expiration, and certificate of analysis were 

documented in the laboratory files: except for the purity provided in revised analysis 

protocol, other information was not provided anywhere. 

Laboratory spreadsheet: 

1. In the on-field sample sheet, all dup A1 should be dup B1. 

2. Two sets of data were the same, but labeled differently. One set were the results in the columns 

of P, Q, and R of each worksheet of the Laboratory spreadsheet_MITC_7_07_Bakersfield.xls file. 

Via phone conversation, these results were from the 10 ppm of the standard solution for 

continuous standard calibration control (as in page 36 of the report). The other set of data was 

actually collected from all the results on the P, Q, and R of each worksheet of the Laboratory 

spreadsheet_MITC_7_07_Bakersfield.xls file and listed on the Standard fortified laboratory 

samples worksheet of the MITC-stds.xls file as the results of the laboratory spike samples 

analyzed with every 10 field samples. 

III. Fieldwork Comments 

Page 14. First Paragraph. This paragraph states that for the evening watering-in periods 

on-field samplers were not run when the sprinklers were running. While this is reasonable to 

avoid damage to the samplers, the study design should have been planned to have sufficient 

off-site samplers to provide a back-calculated estimate of the flux. It is completely unknown how 

much mass loss was missed due to the lack of samplers during the irrigation events. In addition, 

the pump running times for the standard watering-in treatments are not clear. The field history 

sheets are difficult to decipher. 

Page 28. Chemigation Plots (#1 and #2). This paragraph states that Plot #2 was completed at 

10:40 a.m. However, Table 2 indicates that the initial watering-in was finished at 0800 hours. It 

is unclear whether the 10:40 a.m. refers to the completion of setting up the sonic anemometer 

tower rather than the watering-in. 

Page 29. First paragraph. This paragraph states that Appendix F contains confirmatory results 

for periods 3-6. However, Appendix F shows only figures and the heading of Appendix F 

“Confirmatory Modeling versus Measured Plots (Periods 4-6)” is in conflict with the caption of 

the very first plot where is states that the plot is for Period 3. These sorts of mistakes lead to 

doubt about the correctness of the remainder of the report. 

Page 29. Last paragraph. The irrigation paragraph indicates that the irrigation was quite 

variable with the shank applications receiving less water than the planned amount. The authors 

end by saying that if the irrigation is averaged across fields that results were generally close to 
Randy Segawa 

February 26, 2008 

Page 6 

design amounts. However, the authors also provide unsupported speculation that if the shank 

applications had not received 14% to 21% less water than planned that the shank results would 

show even lower emissions. So, the author’s statements are in conflict. Either the average 

amount across fields is acceptable and the variation is judged to not be significant or the shank 

received significantly less, not both. 

Page 34. Tables 7 and 8. Field Fortifications, Blanks, and Duplicates. 

The authors conclude that the field blank and duplicate results are acceptable. However, the Field 

Spike results are quite variable, showing recoveries between 28% and 175%. The Field Blanks 

are contaminated. The Duplicates are not in as close agreement as inferred in the text–for the 

range of concentrations observed in most samples in this study the duplicates differ by an 

average 12%. 

Pages 35–36. Table 9. This table indicates that recoveries for samples with 0.5 ug/tube are 

acceptable. Yet on Page 35 the text states that, based upon Merricks (1999), any on-field tubes 

with 2 ug/tube or less were defaulted to a “flux value” of <1 ug/m2/sec. The flux and the results 

should use all observations above the detection limit for this laboratory (University of California, 

Davis) and this study. 

Page 37. Section 3.0. This section states that Appendix C contains tabular results of all on-field 

and ambient measured concentrations. First, Appendix C is not labeled as such. Second, no 

off-site air concentrations are shown in what appears to be Appendix C. Third, the off-site air 

samples are not ambient samples by DPR definition. Ambient samples are taken to characterize 

regional sub-chronic and chronic exposures. The samples taken in this study represent acute 

exposures and are simply off-site air concentrations. 

Page 37–50. Section 4.0. Section 4.2–the flux is estimated by back-calculation, not the “ambient 

method.” 

Page 43, 44, and 79. The shank emission profile analysis shows 13 of the 18 periods where the 

air concentration profile does not behave according to the assumption of decreasing air 

concentrations with height. The air concentrations for most of these 13 periods are similar to the 

lower concentrations in the sprinkler emission profiles. However, with the exception of the last 

sampling interval, the sprinkler emission profiles do show decreasing air concentrations with 

height. It is noted in review of the laboratory QA/QC that all the sprinkler samples were 

analyzed together over several days followed by all the shank samples analyzed together days 

later. This can lead to systematic laboratory differences that confound results. It cannot be ruled 

out that this occurred in these laboratory analyses and the emission profiles may illustrate that 

problem. Specifically, in the figures on Page 79, there are times when the 3 ft or 1 ft samples 

show air concentrations higher than the 0.5 ft sampler or when the 1 ft sampler shows an air 

concentration higher than the 3 ft sampler. The key sampling period for the shank method on 
Randy Segawa 

February 26, 2008 

Page 7 

field 4 (Period 2), estimated flux with only 2 samples. This is not acceptable. In future studies the 

on-site air concentrations should be measured at more than three levels for the IHF method. That 

way if one sampler is lost the results will still be acceptable. Most IHF studies in the literature 

use at least 5 measurement heights. 

Page 47. Figure 14A. These results seem suspect. For the shank fields the “upwind” air 

concentrations are higher than the on-site concentrations. In addition, the shank on-site air 

concentrations are substantially lower than sprinkler onsite concentrations but the “upwind” 

samplers for shank and sprinkler show concentrations of similar magnitude. It makes no sense 

that off-site air concentrations are higher than those measured on-site (see page 89). This may 

indicate laboratory problems and/or cross-field plot contamination. These field plots were much 

closer than DPR would advise and the potential for cross-field contamination is significant (see 

page 92). The authors may have justified the orientation and spacing of these field plots based on 

consulting prevailing wind patterns in the area. However, prevailing winds mean nothing when 

measuring air concentrations over more than a few hours. This study was conducted over four 

days. 

Page 49. Section 4.6 and Figure 15. The percent of MITC emitted results shown in Figure 15 

were checked using the flux estimates for each sampling interval provided by the authors in an 

Excel spreadsheet. The exact mass loss calculations for all four fields were not provided so it 

was difficult to verify the results shown in Figure 15. The recalculated mass loss estimates were 

slightly different from that shown in Figure 15. There appears to be two reasons for the 

differences: (1) the authors used a conversion of 4.2 pounds of metam sodium per gallon of 

product rather than the label conversion of 4.26 pounds per gallon and (2) it appears that the 

authors used a uniform 75 gallons per acres application rate for all four applications to 

calculation the percent loss. However, both shank applications received less than 75 gallon per 

acres. Thus, the sprinkler mass loss estimates are virtually identical due to the very small 

difference between 4.2 and 4.26 lbs metam sodium per gallon product and the shank estimates 

differ slightly due to both the pounds metam sodium per gallon difference and the difference in 

total mass applied. 

Although comparisons of the sprinkler mass loss results with previous sprinkler studies is 

difficult, the results do seem reasonable based upon trends in those previous studies. 

Comparisons between the results from the sprinkler application in this study and the night 

application studies in DPR database, Wofford (1994) and Sullivan (2006), are difficult because 

the timing of the applications were significantly different. The Wofford application was started at 

1940 hours on August 3, so, the entire application, the watering-in and several hours after were 

under dark hours. This would lead to substantial mass lost, 73.3% loss was observed through the 

first night. The Sullivan (2006) study application was started at 0400 hours and completed after 

sunrise. The first watering-in was applied during daylight hours. Total mass loss in Sullivan 

(2006) was 39.1%. The applications in this report were started at 0100 hours and Table 2 
Randy Segawa 

February 26, 2008 

Page 8 

indicates that the watering-in was completed at 0800 hours. This means that the period following 

the watering in was during daylight. The additional watering-in on the first evening would be 

expected to further reduce the loss. The Wofford loss through the watering-in was 53%, for 

Sullivan (2006) loss through the initial watering-in was 10%. Total loss for this study was about 

37% with a loss through initial watering-in of approximately 13%. 

These shank loss results are not consistent with any of the shank results DPR already has. The 

shank application mass loss result in this study is substantially less than any of the previous 

shank studies. In fact, these shank mass losses are similar to the drip application losses observed 

in Levine et al. (2005), and Li et al. (2006). DPR has no other night shank application data. Other 

than the change in rig, nothing in the report indicates reasons for the extremely small mass loss. 

These extremely low mass loss estimates for night shank application should be verified with a 

second trial before DPR uses these results for VOC calculations. 

Page 51. Conclusions. Each conclusion is discussed below: 

1. Shank injection/compaction . . .produced excellent retention of MITC . . . 

This conclusion cannot be made until the QA/QC issues are resolved. Unfortunately, it is not 

likely laboratory QA/QC issues can be completely resolved. 

2. Relatively small differences were observed between the pulsed and continuous water seals 

for chemigation. 

These results seem internally consistent. It is unlikely corrections for the QA/QC would change 

this conclusion. 

3. The use of on-field profiles and the integrated horizontal flux method produced a high degree 

of precision . . . 

The authors are placing importance on precision to the exclusion of accuracy. The precision of 

these results is unimportant if the accuracy is unacceptable. Even the precision is at issue due to 

the significant QA/QC issues. 

4. In order to quantify very low levels of emissions . . . 

See comments on the detection limit above. There is conflicting information relating to the 

detection and quantification limits. 

5. Nighttime applications based on shank injection . . .well managed off-gassing rates. 
Randy Segawa 

February 26, 2008 

Page 9 

This conclusion cannot be made until the QA/QC issues are resolved. Unfortunately, it is not 

likely laboratory QA/QC issues can be completely resolved. 

6. Nighttime applications using chemigation would benefit by modified water sealing practices 

in order to better retain MITC in the heat of the day . . . 

A field study would need to demonstrate that this additional water application would 

significantly reduce the loss. The first two sampling intervals, as expected, showed the highest 

flux. If the results are taken as they are, the loss in this study is similar to Sullivan (2006). 

IV. Discussion 

Previous studies (Merricks, 1999; Merricks 2001, and Merricks 2002) have indicated that total 

mass loss for sprinkler and shank are similar. This study shows widely differing results between 

sprinkler and shank. The shank applications would be expected to show the same increase in flux 

during the day that was shown by the sprinkler. However, measured air concentrations for shank 

were so low that no trend was demonstrated. A second study should be conducted to confirm that 

the new rig is the reason for the very low emission obtained for shank. Period 2 (the critical 

period) shank flux was estimated using only two points. A simple straight line was fit to 

characterize the concentration profile because one of the three samples was lost. This, in addition 

to the considerable uncertainty in the laboratory QA/QC cast significant doubt on the shank 

results. 

V. Technical Recommendations 

There are two alternatives regarding the data in this report: 

1. Reject the report due to laboratory QA/QC issues and irregularities in the field study conduct. 

This is most defensible from a scientific standpoint and our preference. 

2. Use the mass loss results but add uncertainty factors to the results. The recommended 

uncertainty factors for the VOC program only are as follows: (a) assume the sprinkler mass 

loss is the same as standard sprinkler, and (b) assume the shank mass loss is the same as 

intermittent shank. Acute exposure of persons off-site is not addressed in this review. These 

results are not of sufficient quality to allow an assessment of required acute exposure buffer 

zones for these methods. Use of this alternative is a completely qualitative management 

decision. 

Regardless of which alternative is chosen above, because the shank mass loss reported in this 

study is substantially less than losses observed in any prior shank study, a second field study 
Randy Segawa 

February 26, 2008 

Page 10 

should be conducted to confirm these results. The second study should directly compare the 

standard shank method to the Western Farm rig used in this study. 

VI. Regulatory Recommendations 

If a nighttime application is to be allowed, it must adhere to the specifications used in the 

application studies. Therefore, the following regulatory requirements are recommended for these 

fumigation methods: 

For Night Sprinkler Application with Two Post-Fumigation Water Treatments 

• the field must receive an initial irrigation at a rate of 0.20 inches immediately prior to 

application 

• the application period must be initiated no earlier than 0100 hrs and be applied at a minimum 

rate of 0.20 acre-inches/hour 

• post-fumigation water treatments must be consistent with the requirements described in 

Title 3, California Code of Regulations, section 6450.1(d)(2)

* 

For Night Shank Application with Two Post-Fumigation Water Treatments 

• application must start no earlier than 0100 hours 

• post-fumigation water treatments must be consistent with the requirements described in 

Title 3, California Code of Regulations, section 6450.1(d)(2)

* 

• the following fumigation equipment and procedures must be used 

i. Before application, thoroughly cultivate the field to remove clods with a disc or 

spring tooth bar. Soil must contain adequate moisture (as stated in regulations) prior 

to application 

ii. The application equipment must meet the following criteria: 

The shanks must be set on a single or multiple bars so there is an effective spacing 

of no more than 4 inches between shanks. 

Injection depth is 3 inches, 6 inches, and 9 inches. 

Nitrogen must be used to purge the system before applicator bar is lifted out of 

the ground at any time. 

*

 The 0.20 inches for the post-fumigation water treatments described in the regulations should be changed to 0.40 

inches, so it is consistent with the water treatments for this and previous monitoring studies 
Randy Segawa 

February 26, 2008 

Page 11 

iii. Compaction equipment 

The application tool bar(s) are followed by a ring roller with four gauge wheels 

controlled by hydraulic cylinders to control depth and or pressure to seal the 

chisel trace that is as least as wide as the application tool bar. 

The ring roller will be followed with a coil packer that is as least as wide as the 

application tool bar. 

New Method Codes for Field Fumigation Methods 

Since both application methods are new, the following will be used for the fumigation code on 

the Pesticide Use Reporting and the Field Fumigant VOC Emission Allowance forms: 

Method code Emission Rating (%) Regulation Section Field Fumigation Method 

1452 77 6452 (b)(1) Night Sprinkler/Broadcast or Bed/ 

Two Water Treatments 

1455 28 6452 (b)(1) Night Nontarpaulin/Shallow/Broadcast 

or Bed/ Two Water Treatments 
Randy Segawa 

February 26, 2008 

Page 12 

References 

Levine, J., D. Kim, and P. Lee. 2005. Monitoring an untarped bedded drip application of 

metam-sodium in Merced Country. California Environmental Protection Agency. DPR. 

Environmental Monitoring Branch. 1001 I Street, P.O. Box 4015, Sacramento, California 95812. 

EH05-03. 

Li, L., T. Barry, K. Mongar, and P. Wofford. 2006. Modeling Methyl Isothiocyanate Soil Flux 

and Emission Ratio from a Field following a Chemigation of Metam-Sodium. Journal 

Environmental Quality. Volume 35:707-713. 

Merricks, D.L. 1999. Determination of methyl isothiocyanate offsite air movement from 

application of Metam-sodium through shank injection and sprinkler irrigation. Agrisearch 

Incorporated, 5734 Industry Lane, Fredrick, Maryland 21704-7293. December 14, 1999. 

Merricks, D.L. 2001. Determination of methyl isothiocyanate offsite air movement from 

application of Metam-sodium through shank injection. Agrisearch Incorporated, 5734 Industry 

Lane, Fredrick, Maryland 21704-7293. March 1, 2001. 

Merricks, D.L. 2002. Determination of methyl isothiocyanate offsite air movement from 

application of Metam-sodium through sprinkler irrigation. Agrisearch Incorporated, 5734 

Industry Lane, Fredrick, Maryland 21704-7293. January 10, 2002. 

Sullivan, D. 2006. Field volatility of MITC after application of metam-sodium at the Edison 

Road field site, Mettler, California. Department of Pesticide Regulation registration volume 

number 50150-0163. 

Wofford, P., K.P. Bennett, J. Hernandez, and P. Lee. 1994. Air Monitoring for Methyl 

Isothiocyanate During a Sprinkler Application of Metam-Sodium. 1994. California 

Environmental Protection Agency. DPR. Environmental Monitoring Branch. 1001 I Street, P.O. 

Box 4015, Sacramento, California 95812. EH94-02. 
Randy Segawa 

February 26, 2008 

Page 13 

Figure 1. Recoveries of the laboratory spikes in analysis sequence 

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

100 

110 

0 10 20 30 40 50 

Analysis sequence 

% recovery 
Randy Segawa 

February 26, 2008 

Page 14 

Figure 2. One copy of standard curves for laboratory analysis data calculation in Bakersfield 

study, 2007 

7/31/07 Mitc Standard Curve 

y = 1.8509x 

R2

 = 0.9793 

0 

5 

10 

15 

20 

25 

30 

35 

40 

Corrected Area 

0 5 10 15 20 25

PPM 
Randy Segawa 

February 26, 2008 

Page 15 

Figure 3. A typical MITC standard curve from the California Department of Food and 

Agriculture ’s laboratory analysis 
BEFORE THE DIRECTOR OF THE 

DEPARTMENT OF PESTICIDE REGULATION 

STATE OF CALIFORNIA 

In the Matter of Grimmway Farms 

Request for Approval of 

Reduced Volatile Organic Compound 

Emissions Field Fumigation Methods 

DECISION

(Title 3, California Code of Regulations section 6452) 

GRIMMWAY FARMS 

Mr. Sean McNally 

Vice President 

Corporate and Government Affairs 

14141 Di Giorgio Road 

P.O. Box 81498 

Bakersfield, California 93380-1498 

______________________________/ 

Summary 

Grimmway Farms submitted a request to allow chemigation applications of metam-sodium and 

metam-potassium (methyl isothiocyanate [MITC]-containing pesticides) based on a study 

previously submitted to the Department of Pesticide Regulation (DPR). The Metam-Sodium 

Task Force and Amvac Chemical Corporation submitted a study to DPR titled “Field Volatility 

of MITC After Application of Metam-Sodium at the Edison Road Field Site, Mettler California” 

dated July 2006. The application was made by chemigation with a 4:00 a.m. start time, 

which qualifies as a night application. As part of DPR’s efforts to reduce volatile organic 

compound (VOC) emissions, most night applications of MITC-containing pesticides are 

prohibited within several ozone nonattainment areas (NAAs) during May–October, under Title 3, 

California Code of Regulations (3 CCR) section 6450.1(c). However, the regulations also 

include a provision for DPR’s Director to grant interim approval of fumigation methods that 

reduce VOC emissions (3 CCR section 6452). DPR has completed its evaluation of the 

fumigation method described in the study as specified in 3 CCR section 6452. The DPR has 

determined that with application rate modifications the method meets the standard for approval 

as an interim method, as described below. Effective August 1, 2008, DPR grants approval for 

interim use of the metam 4:00 a.m. start chemigation method described in the study in all five 

ozone NAAs. The method described in the study may be used for three years from the effective 

date. 

Background 

VOCs contribute to the formation of ozone, a major air pollutant in several regions of California. 

California’s State Implementation Plan for the federal Clean Air Act ozone standard includes an 
Grimmway Farms 

Page 2 

element to track and reduce VOC emissions from pesticides. On January 25, 2008, DPR adopted 

regulations to control VOC emissions from fumigants during the May–October peak ozone 

season in five ozone NAAs: Sacramento Metro, San Joaquin Valley, Southeast Desert, 

South Coast, and Ventura. The regulations include provisions that only allow fumigation 

methods for which DPR has adequate data to determine the VOC emission rates. However, the 

regulations include a provision for interim approval of fumigation methods with emissions no 

greater than the field fumigation methods allowed in the regulations in the respective areas 

(3 CCR section 6452). 

On June 16, 2008, DPR received a verbal request from representatives of Grimmway Farms and 

other carrot growers to approve an interim method for nighttime chemigation applications using 

metam-potassium and metam-sodium. DPR received a subsequent written request from 

Grimmway Farms on July 31, 2008. The fumigation method is critical to carrot and potato 

farming operations since a label restriction regarding ambient air temperature limits the times of 

day that the pesticide may be applied in certain regions of California. Between this label 

restriction and the prohibition of nighttime chemigation, growers in NAAs have a narrow 

window to treat their acreage. 

Regulatory Standards and Considerations 

Title 3, CCR section 6452 sets different standards by which to evaluate whether a new 

fumigation method will be allowed, one for the Sacramento Metro and South Coast ozone 

NAAs and one for the San Joaquin Valley, Southeast Desert, and Ventura ozone NAAs. 

Sacramento Metro and South Coast have a less stringent standard because no further VOC 

reductions from pesticides are needed in these ozone NAAs. Both “low-emission” and 

“high-emission” methods can be used in these two areas. Only “low-emission” methods are 

allowed in the San Joaquin Valley, Southeast Desert, and Ventura ozone NAAs during the 

May–October peak ozone season. The key information is the emission rating (percent of the 

fumigant applied that is emitted to the air) and the emission rate (emission rating multiplied by 

the maximum application rate). Either the emission rating or the emission rate can be no greater 

than the current methods allowed within the ozone NAAs by the regulations. The following table 

shows the standard for approval of an interim method for MITC-generating pesticides, based on 

DPR’s current emission estimates. 

Ozone NAA 

Maximum Allowed 

MITC Emission Rating 

(percentage) 

Maximum Allowed 

MITC Emission Rate 

(pounds/acre) 

Sacramento Metro, South Coast 77 140 

San Joaquin Valley, Southeast 

Desert, Ventura 28 51 
Grimmway Farms 

Page 3 

In assessing whether the new method meets the standard, DPR must assess the scientific data 

submitted to establish the emission rating, normally consisting of field monitoring data. In 

evaluating this data, 3 CCR section 6452 requires DPR to consider the following factors: 

• whether the information is sufficient to estimate emissions. 

• whether the results are valid as indicated by the quality control data. 

• whether the conditions studied represent agricultural fields. 

Summary and Evaluation of the Submitted Information 

The Metam-Sodium Task Force and Amvac Chemical Corporation submitted a study to DPR 

titled “Field Volatility of MITC After Application of Metam-Sodium at the Edison Road Field 

Site, Mettler California” dated July 2006. The application was made by chemigation with a 

4:00 a.m. start time, which qualifies as a night application. AMVAC Metam 42 (Metam Sodium 

42 percent w/w) was applied at a rate of 75.35 gallons/acre (319.5 lbs active ingredient/acres) by 

sprinkler (chemigation) to a 10.17-acre field. The application was finished at 10:00 a.m. After a 

15 minute flushing of the sprinkler lines with water a “water cap” of 0.23 acre inch was applied 

between 10:15 a.m. and 11:30 a.m. This application method also includes an additional “water 

cap” of 0.46 acre inch between 6:00 p.m. and 8:30 p.m. 

Twenty air samplers were positioned off-site at distances of 30 meters to 150 meters from the 

field edge. The Quality Control/Quality Assurance results were reviewed and found to be 

acceptable. A four-day MITC flux profile was developed and total MITC mass loss was 

estimated using the ISCST model and the back-calculation method in two different ways: 

• using all 20 air samplers: 283.1kg MITC mass loss/33.79 percent and 61.1 pounds/acre. 

• using only the 12 forecast samplers (samplers expected to be downwind): 292.71kg MITC 

mass loss/34.93 percent and 63.2 pounds/acre. 

Findings 

The information provided indicates that the emissions for this fumigation method are 

approximately 35 percent of the available MITC. Therefore, DPR has assigned the following 

emission ratings to this method: 

• metam-sodium and metam-potassium sprinkler 4:00 a.m. start method: 35 percent. 

Low-emission application methods must achieve an emission rating of 28 percent or less. 

Therefore, this application method cannot be considered a low-emission method based upon 

the emission rating. However, this method can be considered a low-emission method if the 

maximum application rate is adjusted to a level that ensures the emission rate (emission rating 
Grimmway Farms 

Page 4 

multiplied by the maximum application rate) does not exceed 51 pounds of MITC per acre, 

equivalent to 290 pounds of metam-potassium active ingredient (A.I.) per acre or 260 pounds of 

metam-sodium A.I. per acre. Table 1 shows the equivalent product application rates. 

Conclusions 

The 35 percent emission rating and an application rate limit support approval of this fumigation 

method. Effective August 1, 2008, the metam sprinkler 4:00 a.m. start application method is 

approved for use in the San Joaquin Valley, Southeast Desert, and Ventura ozone NAAs with the 

following restrictions during May 1–October 31: 

• metam-potassium application rate must not exceed 290 pounds A.I. per acre. 

• metam-sodium application rate must not exceed 260 pounds A.I. per acre. 

• fumigations must start no earlier than 4 a.m. 

• two post-fumigation water treatments as specified in 3 CCR section 6450.1(d)(2) must be 

applied. 

• pesticide use reports must identify these applications using field fumigation method 

 code 1472. 

Effective August 1, 2008, the metam sprinkler 4:00 a.m. start application method is approved for 

use in the Sacramento Metro and South Coast ozone NAAs with the following restrictions during 

May 1–October 31: 

• fumigations must start no earlier than 4:00 a.m. 

• two post-fumigation water treatments as specified in 3 CCR section 6450.1(d)(2) must be 

applied. 

• pesticide use reports must identify these applications using field fumigation method 

 code 1472. 

The only restriction, other than labeling requirements, outside the May 1–October 31 period is to 

include field fumigation method code 1472 on pesticide use reports. 

DPR grants interim approval of this fumigation method for three years from the effective date. 

By: __ ___ Date: _____08/14/2008_____ 

 Mary-Ann Warmerdam, Director 

Attachment 
Table 1. Maximum product application rates in gallons per acre to meet low emission MITC mass loss criteria of 

acre in the San Joaquin Valley, Southeast Desert, and Ventura NAAs during May–October. 

Metam Sodium Products 

Company Product Name Reg No. lbs A.I./gal Conversion factor1 Maxim

AMVAC AMVAC Metam 5481-420-AA 3.18 0.8163 AMVAC AMVAC Metam 426 5481-423-AA 4.26 1.0935 AMVAC METAM SODIUM 5481-350-ZA 3.18 0.8163 AMVAC VAPAM 5481-466-AA 3.18 0.8163 AMVAC VAPAM HL 5481-468-AA 4.26 1.0935 

Buchman 

Laboratory BUSAN 1020 1448-85-AA 3.2 0.8214 

Taminco, Inc. Metam CLR 42% 45728-16 4.25 1.0909 

TessenderloKerley, Inc. SECTAGON 42 61842-6 4.22 1.0832 

Metam Potassium Products 

Company Product Name Reg No. lbs A.I./gal Conversion factor Maxim

AMVAC K-PAM HL 5481-483-AA 5.8 1.3154 

TessenderloKerley, Inc. SECTAGON-K54 61842-7-AA 5.8 1.3154 

1 73 . . 1 * *

129 . . 2.2046

product lb MS MITCmol wt kg conversion factor gal MSmol wt lbs =

2 allowed application rate = (65.7kg MITC/ac)/(conversion factor) 
BEFORE THE DIRECTOR OF THE 

DEPARTMENT OF PESTICIDE REGULATION 

STATE OF CALIFORNIA 

In the Matter of Ratto Brothers, Inc. 

Request for Approval of 

Reduced Volatile Organic Compound 

Emissions Field Fumigation Method 

DECISION

(California Code of Regulations, Title 3, section 6452) 

RATTO BROTHERS, INC. 

Mr. Raymond A. Ratto, Jr. 

Ratto Brothers, Inc. 

6312 Beckwith Road 

Modesto, California 95358 

Summary 

Ratto Brothers, Inc., submitted a request to allow drench applications of potassium N-methyl 

dithiocarbamate (metam-potassium). As part of the Department of Pesticide Regulation’s (DPR’s) 

efforts to reduce volatile organic compound (VOC) emissions, this fumigation method is not 

allowed within several ozone nonattainment areas (NAAs) during May–October, under Title 3, 

California Code of Regulations (3 CCR) section 6450.1(c). However, the regulations include a 

provision for the DPR Director to grant interim approval of fumigation methods with emissions no 

greater than the field fumigation methods allowed in the regulations (3 CCR section 6452). DPR 

has completed its evaluation of the fumigation method as specified in 3 CCR section 6452. No data 

was submitted, but even assuming 100 percent VOC emissions, the application rate is low enough 

to meet the requirements for approval as an interim method. Effective immediately, DPR grants 

approval for interim use of the drench application method using either metam-potassium or 

metam-sodium, with limits on the application rate. The emission rating assigned to this method is 

100 percent. This method may be used for three years from the date of this decision. Continued use 

beyond three years is contingent on the submittal of an acceptable study to document the emissions 

from this fumigation method. 

Background 

VOCs contribute to the formation of ozone, a major air pollutant in several regions of California. 

Under the federal Clean Air Act, California’s State Implementation Plan for ozone includes an 

element to track and reduce VOC emissions from pesticides. On January 25, 2008, DPR adopted 

regulations to control VOC emissions from fumigants during the May–October peak ozone 

season in five ozone NAAs: Sacramento Metro, San Joaquin Valley, Southeast Desert, 

South Coast, and Ventura. The regulations include provisions that only allow fumigation 

methods for which DPR has adequate data to determine the VOC emission rates. However, the 
Ratto Brothers, Inc. 

Page 2 

regulations include a provision for interim approval of fumigation methods with emissions no 

greater than the field fumigation methods allowed in the regulations in the respective areas 

(3 CCR section 6452). 

In a letter dated April 24, 2008, Ratto Brothers, Inc., requested that DPR approve an exemption 

for a soil drench application method using potassium N-methyl dithiocarbamate (metampotassium; methyl isothiocyanate [MITC]-generating pesticide). The fumigation method is 

critical to Ratto Brothers farming of specialty crops like leafy green vegetables, herbs, and root 

vegetables because most other pesticide products are not registered for use on these crops. 

Ratto Brothers, Inc., asserts that other fumigation methods allowed probably have higher 

VOC emissions. 

Regulatory Standards and Considerations 

Section 6452, 3 CCR, sets different standards by which to evaluate whether a new fumigation 

method will be allowed; one for the Sacramento Metro and South Coast ozone 

NAAs, and one for the San Joaquin Valley, Southeast Desert, and Ventura ozone NAAs. 

Sacramento Metro and South Coast have a less stringent standard because no further VOC 

reductions from pesticides are needed in these ozone NAAs. Both “low-emission” and “highemission” methods can be used in these two areas. Only “low-emission” methods are allowed in 

the San Joaquin Valley, Southeast Desert, and Ventura ozone NAAs during the May–October 

peak ozone season. The key information is the emission rating (percent of the fumigant applied 

that is emitted to the air) and the emission rate (emission rating multiplied by the maximum 

application rate). Either the emission rating or the emission rate can be no greater than the 

current methods allowed within the ozone NAAs by the regulations. The following table shows 

the standard for approval of an interim method for MITC, based on DPR’s current emission 

estimates. 

Ozone Nonattainment Area 

Maximum Allowed 

MITC Emission Rating 

(percentage) 

Maximum Allowed 

MITC Emission Rate 

(pounds/acre) 

Sacramento Metro, South Coast 77 140 

San Joaquin Valley, Southeast 

Desert, Ventura 28 51 
Ratto Brothers, Inc. 

Page 3 

In assessing whether the new method meets the standard, DPR must assess the scientific data 

submitted to establish the emission rating, normally consisting of field monitoring data. In 

evaluating this data, 3 CCR section 6452 requires DPR to consider the following factors: 

• whether the information is sufficient to estimate emissions. 

• whether the results are valid as indicated by the quality control data. 

• whether the conditions studied represent agricultural fields. 

Summary and Evaluation of the Submitted Information 

Ratto Brothers, Inc., proposes to apply K-Pam (metam-potassium) using a drench application 

method. K-Pam label requirements for this method include pre-irrigation to achieve 50 to 80 

percent field capacity and an application rate of 30 to 60 gallons of K-Pam per treated acre. 

Ratto Brothers, Inc., applies K-Pam using low-pressure booms with nozzles 9 to 10 inches above 

the top of the beds at a rate of 15 to 23 gallons of K-Pam in 1,900 gallons of water per acre. 

However, additional information from Ratto Brothers, Inc., indicates that their application rate is 

on a broadcast acre basis, not treated acre basis. Applications are made in the early morning and 

are followed by a 0.15 to 0.20-inch water treatment within 30 minutes of the application and 

three additional water treatments over the first 24 hours. Ratto Brothers, Inc., proposes to 

fumigate up to 15 acres per day for a total of 1,000 to 1,500 acres using this method. 

NOTE: The application rates described in this document are based on broadcast applications, 

unless otherwise noted. Drench applications are normally applied to beds or rows, and labels 

frequently refer to application rates on a treated acre basis. Application rates on a treated acre 

basis must be converted to the broadcast equivalent (bed/row treated area plus furrow untreated 

area) to determine compliance with specified application rate limits. 

Ratto Brothers, Inc., did not submit any data documenting the VOC emissions ratings associated 

with a MITC drench application. DPR is not aware of any emissions data for this fumigation 

method. In addition, this method is substantially different from any other fumigation method 

with available data. DPR staff are not confident in using other data as a surrogate for this 

fumigation method. However, the proposed application rate is very low. Even if the emission 

rating is 100 percent, the VOC emission rate would range from 43 to 66 pounds of VOCs 

per broadcast acre, depending on the application rate. A metam-potassium application rate of 

98 pounds active ingredient per broadcast acre (17 gallons/acre of K-Pam) would be equivalent 

to the San Joaquin Valley’s maximum allowed MITC emission rate of 51 pounds of VOCs per 

broadcast acre. 
Ratto Brothers, Inc. 

Page 4 

Findings 

Ratto Brothers, Inc., did not submit any data documenting the VOC emissions associated with a 

MITC drench application and no data is available to reliably estimate the emission rating. 

Therefore, the emission rating assigned to MITC drench applications is 100 percent. 

Conclusions 

The 100 percent emission rating and proposed application rate of 87 to 133 pounds active 

ingredient per broadcast acre of metam-potassium support approval of this fumigation method. 

Effective immediately, the MITC drench application method is approved for use in the 

San Joaquin Valley, Southeast Desert, and Ventura ozone NAAs with the following restrictions 

during May 1–October 31: 

• Metam-potassium application rate must not exceed 98 pounds active ingredient per acre. 

• Metam-sodium application rate must not exceed 90 pounds active ingredient per acre. 

• Soil moisture at the time of application must meet the requirements described in 

 3 CCR section 6450.1(b). 

• Fumigations must start no earlier than one hour after sunrise and must be completed no later 

than one hour before sunset. 

• Two post-fumigation water treatments as specified in 3 CCR section 6450.1(d)(2)(A) must 

be applied. 

• Pesticide use reports must identify these applications using field fumigation method 

 code 1413. 

Effective immediately, the MITC drench application method is approved for use in the 

Sacramento Metro and South Coast ozone NAAs with the following restrictions during 

May 1–October 31: 

• Metam-potassium application rate must not exceed 270 pounds active ingredient per acre. 

• Metam-sodium application rate must not exceed 246 pounds active ingredient per acre. 

• Soil moisture at the time of application must meet the requirements described in 

 3 CCR section 6450.1(b). 

• Fumigations must start no earlier than one hour after sunrise and must be completed no later 

than one hour before sunset. 

• Two post-fumigation water treatments as specified in 3 CCR section 6450.1(d)(2)(A) must 

be applied. 

• Pesticide use reports must identify these applications using field fumigation method 

 code 1413. 
Ratto Brothers, Inc. 

Page 5 

The only restriction, other than labeling requirements, outside the May 1–October 31 period is to 

include field fumigation method code 1413 on pesticide use reports. 

DPR grants interim approval of this fumigation method for three years from the date of this 

decision. Continued use of this fumigation method beyond three years is contingent on the 

submittal of an acceptable study to document the emissions. Since DPR must adopt regulations 

to include these new methods prior to the expiration of the interim approval, the study should be 

submitted within 12 months. DPR recommends that Ratto Brothers, Inc., submit a draft protocol 

for DPR scientific staff review prior to initiating the study. 

By: _______ ___for______________ Date: _____05/15/08______ 

 Mary-Ann Warmerdam, Director 

 Department of Pesticide Regulation 
Department of Pesticide Regulation 

Mary-Ann Warmerdam 

Director M E M O R A N D U M Arnold Schwarzenegger 

Governor 

1001 I Street • P.O. Box 4015 • Sacramento, California 95812-4015 • www.cdpr.ca.gov

A Department of the California Environmental Protection Agency 

TO: John S. Sanders, Ph.D. 

Environmental Program Manager II 

 Environmental Monitoring Branch 

 Original signed by Pam Wofford 

FROM: Randy Segawa for 

Environmental Program Manager I 

 Environmental Monitoring Branch 

 916-324-4137 

 Terrell Barry, Ph.D., Research Scientist III Original signed by 

Environmental Monitoring Branch 

DATE: April 29, 2010 

SUBJECT: METHYL IODIDE (IODOMETHANE) MITIGATION EVALUATION AND 

OPTIONS 

Summary 

The Department of Pesticide Regulation’s (DPR’s) risk assessment for methyl iodide describes 

several exposure scenarios of concern, including exposure to bystanders. DPR’s Environmental 

Monitoring Branch (EMB) staff evaluated several alternatives to reduce methyl iodide bystander 

exposure to acceptable levels. The evaluation included an assessment of fumigations using 

virtually impermeable film (VIF) to suppress emissions. EMB staff found that three 

methyl iodide studies using VIF likely underestimate the air concentrations and flux, and use 

poor methodology, as indicated by the quality control results. In addition, the studies did not 

include measurements during tarp cutting or removal. Despite the study problems, changing from 

standard tarps to VIF likely reduces methyl iodide flux 30–40 percent (%). The registrant (Arysta 

LifeScience North American Corporation; Arysta) estimates a 68% reduction due to VIF based 

on the studies. EMB staff estimated buffer zones for various application methods. Restrictions to 

mitigate potential groundwater contamination by iodide breakdown product may be needed. 

Background 

Methyl iodide is a soil fumigant pesticide used prior to planting agricultural fields for controlling 

a variety of pests including weeds, nematodes, insects, and diseases. DPR is considering four 

products for registration: Midas EC Gold (33% methyl iodide, 62% chloropicrin); Midas 33:67 

(33%methyl iodide, 67% chloropicrin); Midas 50:50 (50% methyl iodide, 50% chloropicrin); 

and Midas 98:2 (98% methyl iodide, 2% chloropicrin). This evaluation does not address 

mitigation of chloropicrin. DPR’s risk assessment for methyl iodide describes several exposure 

scenarios of concern, including exposure to bystanders. EMB staff evaluated various options to 

reduce bystander exposure to methyl iodide. Due to its volatility, the main route of exposure is 

inhalation. Similar to mitigation for other fumigants, the primary measures to reduce bystander 
John S. Sanders, Ph.D. 

April 29, 2010 

Page 2 

exposure is to modify application methods and/or implement buffer zones. Both mitigation 

measures are normally based on air monitoring data, specifically studies that determine the flux 

or emission rate from treated fields. Flux estimates are used in conjunction with weather data 

and computer modeling to estimate downwind air concentrations for various scenarios. For 

methyl iodide, Arysta conducted several studies that include VIF to reduce flux. As potential 

mitigation measures, the VIF studies were not previously reviewed or included in the risk 

assessment. 

Virtually Impermeable Film Study Reviews 

Arysta conducted three studies that included direct and indirect flux measurements for 

methyl iodide applications that use VIF. Methyl iodide was applied with a Symmetry tractor 

using a bed-shank method, and three different VIF tarps. Studies were done in Dover, Florida, 

January 2007; Bainbridge, Georgia, March 2007; and Hart, Michigan, May 2007. While out of 

state, the study conditions were similar to California. Arysta determined that these three studies 

had an average peak 24-hour flux of 11 ug/m2

-sec normalized to a 100 lbs/acre application rate 

(8.5% of the amount applied). In comparison, three other Arysta studies of a standard tractor rig 

and standard tarp had an average peak 24-hour flux of 74 ug/m2-sec normalized to a 100 lbs/ac 

application rate (57% of the amount applied). Arysta believes these studies demonstrate that 

Symmetry and VIF combined reduce methyl iodide flux by 85 percent (difference between 74 

and 11 ug/m2-sec) and that 80% of the reduction is due to VIF. Arysta estimates that VIF reduces 

flux by 68% compared to standard tarps. 

Environmental Monitoring Branch’s Staff Review of the Three Methyl Iodide Virtually 

Impermeable Film Studies Indicates Several Major Issues 

Breakthrough–There appears to be significant breakthrough from the front sampling bed to the 

back sampling bed. Not all back sections were analyzed. Arysta believes this is due to 

contamination of the back sections during storage. Arysta provided additional information for 

this explanation, but the data are not conclusive. Specifically, some of the front and back sections 

were stored together and analyzed at the same time. It is unlikely that the back sections were 

contaminated, but the front sections were not. No field blanks were collected that would provide 

conclusive evidence of contamination. 

Spikes and recovery adjustment–The lab spikes were prepared in an unusual manner and do not 

indicate method performance. Trapping efficiency and field spikes were variable, ranging from 

64% to 86% recovery. The trapping efficiency tests may overestimate recoveries because they 

were run for 6 hours. Most field samples were run for 12 hours. Field sample results were not 

adjusted for trapping efficiency or field spike recoveries. 
John S. Sanders, Ph.D. 

April 29, 2010 

Page 3 

Storage stability - Storage stability results were variable, with recoveries ranging from 47% to 

76% after one week. Sample extracts of back sections were held much longer than the storage 

stability test duration. 

Field results–Some results were atypical. Highest concentrations for methyl iodide and 

chloropicrin sometimes occurred at different locations. The unusual results may be due to poor 

sampler placement. Some of the chloropicrin results were very unusual and cannot be used to 

determine the flux. The tarps were not cut or removed during the studies. The flux calculations 

were not checked. 

EMB staff found that the studies likely underestimate the air concentrations and flux, and used 

poor methodology. 

Virtually Impermeable Film Flux Estimation 

Despite the problems with the studies, it is possible to use them to estimate the maximum 

possible flux for VIF applications. EMB staff have not verified the flux calculations, but even if 

there are some errors, they would have little or no impact on the relative adjustments described 

below. Table 1 shows the fluxes estimated by Arysta. 

Table 1. Methyl iodide flux estimated by Arysta for Symmetry bed-shank VIF method, assuming 

100 lbs/acre application rate (Exponent memo dated 2/1/10). 

24-hr peak flux for 100 lbs/ac app rate Study ug/m2

-sec lbs/ac-day % of applied

Total flux 

(lbs/ac and % of applied) 

FL 15.6 12 12 29 

GA 10.9 8.4 8.4 23 

MI 6.5 5.0 5.0 33 

Average 11.0 8.5 8.5 28 

Max possible flux 

estimated by 

DPR* 

38.9 30 30 100 

*Max possible flux estimated by adjusting the average measured flux by 3.57x, increasing the 

total flux from 28 to 100% of the amount applied and increasing the 24-hour peak flux from 8.5 

to 30% of the amount applied. 

A reliable adjustment to account for breakthrough, spike recoveries, and storage stability cannot 

be determined. A maximum worst-case flux can be estimated by assuming that the total flux is 

100% of the amount applied. For example, if the application rate is 100 lbs/acre, the total flux is 

100 lbs/acre over the entire 6-day study period. This is 3.57x higher than the 28 lbs/acre total 
John S. Sanders, Ph.D. 

April 29, 2010 

Page 4 

flux estimated by Arysta as the average for the three VIF flux studies. Applying the same 3.57x 

adjustment factor increases the average 24-hour peak flux value from 11.0 ug/m2-day 

(8.5 lbs/acre or 8.5% of the amount applied) to 38.9 ug/m2-day (30 lbs/ac-day or 30% of the 

amount applied). The maximum worst-case 24-hour peak flux for methyl iodide applied with the 

bed-shank method using a Symmetry rig and VIF is 30 percent of the amount applied. For 

comparison, Table 2 shows the fluxes estimated by Arysta (and verified by EMB staff) for the 

other studies. 

Table 2. Methyl iodide flux estimated by Arysta (and verified by EM, except as noted) for all 

studies. 

Location Fumigation Method Peak 24-hr Flux 

(% of applied) 

Total Flux 

(% of applied) 

Manteca, CA Broadcast-shank, std tarp 51 93 

Watsonville, CA Broadcast-shank, std tarp 35 57 

Guadalupe, CA Bed-shank, std tarp 60 96 

Oxnard, CA Bed-shank, std tarp 54 102 

Plant City, FL* Bed-shank, std tarp 56 71 

Camarillo, CA Drip, std tarp 50 83 

La Selva Beach, CA Drip, std tarp 42 62 

Guadalupe, CA Drip, std tarp 71 100 

Average Broadcast-shank, std tarp 43 75 

Average Bed-shank, std tarp 56 98 

Average Drip, std tarp 54 82 

Average 

(estimated by Arysta) Bed-shank, Symmetry, VIF 8.5 28 

Average 

(estimated by EM) Bed-shank, Symmetry, VIF 30 100 

* Plant City flux not included in the average due to rainfall and other problems with the study. 

However, this makes little or no difference in the average flux estimate. 

The average 24-hour peak flux from two bed-shank studies (Guadalupe and Oxnard) that used 

standard tractor rigs and standard tarps was 56% of the amount applied (74 ug/m2-sec for a 

100 lbs/ac application rate). Therefore, the combined effect of the Symmetry rig and VIF 

reduced the 24-hour peak flux from 56% of the amount applied to no more than 30% of the 

amount applied (74 ug/m2

-sec to 39 ug/m2-sec). The difference between the two values is a 

47% reduction in flux. The relative contribution of the Symmetry rig and VIF to flux reduction 

cannot be determined with the available data, but the majority of the reduction is likely due to 
John S. Sanders, Ph.D. 

April 29, 2010 

Page 5 

VIF. Changing from standard tarps to VIF (without Symmetry rig) may reduce methyl iodide 

flux between 30 and 40%. 

All of these estimates are consistent with the variation in the apparent VIF reduction for 

other fumigants. Arysta provided a list of VIF studies for other fumigants, but most of these 

studies used chambers or other unacceptable methods to measure flux (Arysta note dated 

February 24, 2010). Similarly, tarp permeability data provided by Arysta cannot be used to 

estimate flux under field conditions. Lab permeability measurements indicate that VIF flux 

should be several orders of magnitude lower than standard tarps. Field studies show less than 10x 

reduction. Table 4 summarizes the flux reduction measured for other field studies that likely used 

acceptable flux measurement methods. Complete reports are not yet available, so none of these 

studies have been reviewed or accepted. 

Table 4. Approximate flux reduction from other VIF field studies. Reduction based on difference 

between two nearby simultaneous plots, one with standard tarp and one with VIF. 

Location/Year Fumigant Fumigation Method VIF Reduction of 

Peak Flux (%) 

Santa Maria 2006 Chloropicrin Drip VIF 68 

Salinas 2007 Chloropicrin Drip VIF 88 

Oxnard 2007 1,3-D Drip VIF 44 

Oxnard 2007 Chloropicrin Drip VIF 70 

Salinas 2008 Methyl bromide Drip TIF* 37 

Salinas 2008 Chloropicrin Drip TIF* 33 

Wasco 2009 Methyl bromide Broadcast shallow shank TIF* 66 

Wasco 2009 Chloropicrin Broadcast shallow shank TIF* 19 

Ventura 2009 1,3-D Broadcast shallow shank TIF* 25 

Ventura 2009 Chloropicrin Broadcast shallow shank TIF* 44 

* TIF – totally impermeable film 

Flux estimates for all fumigation methods 

EMB previously reviewed and verified Arysta’s flux estimates for the standard fumigation 

methods. EMB’s review of the VIF studies are described above. Table 5 summarizes the flux 

estimates, including various assumptions of the reduction due to VIF. 
John S. Sanders, Ph.D. 

April 29, 2010 

Page 6 

Table 5. Estimates of flux for each fumigation method and various assumptions of reduction due 

to VIF. 

Fumigation 

Method 

Flux with 

Standard Tarp 

(% of applied) 

Flux with 30% 

VIF Reduction 

(% of applied) 

Flux with 40% 

VIF Reduction 

(% of applied) 

Flux with 50% 

VIF Reduction 

(% of applied) 

Broadcastshallow shank 43 30 26 22 

Bed-shallow 

shank 56 39 34 28 

Drip 54 38 32 27 

Auger probe Not determined Not determined Not determined Not determined 

Buffer zones 

EMB staff calculated approximate buffer zones for several application methods, with standard 

tarps and with VIF. Buffer zones were calculated with the PERFUM model. The PERFUM 

model buffer zones are the 95th percentile maximum direction buffer zones calculated using 

mean flux profiles and 5 years of Ventura weather data. Flux profiles developed by Arysta for 

each of the seven accepted studies were used (Table 2). The mean flux profiles were developed 

for each application method as follows: (1) each flux profile used was aligned with 0800 hours 

and (2) the flux for each hour was averaged. The average flux profile was input into PERFUM 

and the 95th percentile maximum direction buffer zone for desired application rates of each 

application method were determined. The buffer zone distances using PERFUM for a 24-hour 

target concentration of 32 parts per billion (ppb) (C. Andrews, personal communication) are 

shown in Attachment 1. 

Buffer zones for auger probe applications (tree and vine replacement) cannot be determined due 

to lack of monitoring data. It is likely that the flux is approximately the same as a standard 

shallow shank injection method. Auger probe applications are deeper than shallow shank 

(12 inches versus. 18-24 inches), but without a tarp. The label does not clearly state the number 

of applications allowed. It appears that the maximum number is 53 sites and 106 pounds per acre 

(2 pounds per injection site, and injection site every 100 square feet). Determining the 

appropriate buffer zone is more difficult than the other application methods due to the uneven 

number of sites treated across a field. There are at least three buffer zone alternatives for auger 

probe applications. (1) Use the same buffer zones as broadcast-shallow shank or bed-shallow 

shank applications, (2) Limit the number of auger probe applications, and (3) Establish the same 

buffer zone around each individual injection site. 
John S. Sanders, Ph.D. 

April 29, 2010 

Page 7 

The monitoring data indicates that peak concentrations occur within the first two days of 

fumigation, and flux is minimal on later days, including the day standard tarps are cut. Air 

concentrations at the edge of treated areas should be less than the 32 ppb target concentration 

two days after fumigation. The 48-hour buffer zone duration specified on labels should be 

sufficient, assuming the flux is minimal when VIFs are cut (see next section). 

DPR’s methyl bromide regulations specify that two nearby fumigations should be combined to 

determine the buffer zone, if the fumigations are separated by less than 1320 feet (1/4 mile) or 

36 hours. EMB staff determined this separation distance based on consistency of wind direction 

and the probability of the plumes from two 40-acre fields would overlap a significant period of 

time. Air concentrations should be less than the 32 ppb target concentration with the same 

separation requirements, assuming the treated field size is no more than 40 acres. The proposed 

label requirement to prohibit overlapping buffer zones would likely provide adequate separation 

if the minimum buffer zone is large enough and the field size is less than 40 acres. 

Virtually Impermeable Film Tarp Cutting and Removal 

The other main shortcoming with the VIF studies is the lack of measurements during tarp cutting 

and removal, for both flux and worker exposure. Several of the VIF studies listed above show a 

secondary peak of emissions when tarps are cut. Buffer zones or worker protection measures 

may be needed when tarps are cut. Arysta provided air concentration measurements under VIF 

from a separate study (Arysta memorandum dated March 14, 2010). These data have minimal 

value due to small plot size, unusual methods to measure air concentrations, and lack of quality 

control data. Air concentrations under the tarps reached no detectable levels ten days after 

application for each of the seven types of VIF measured. Two studies monitored both soil 

concentrations and air concentrations following applications using standard tarps. Emission rates 

were also estimated. Those results are discussed in a separate memoranda by Barry dated 

April, 29, 2010 and indicate that after 14 days for a standard tarp application that both soil 

concentrations and emissions are minimal. It is possible that the half-life of MeI in the soil will 

be longer for applications using VIF tarps. A longer soil half-life may lead to higher emission 

rates when the tarp is cut and/or removed. 

Groundwater 

As described in the risk assessment, EMB’s evaluation indicates virtually no possibility of 

groundwater contamination by methyl iodide. The groundwater contamination by the iodide 

anion breakdown product is uncertain due to the lack of adequate field dissipation data, but 

potentially high based on a conservative mass-balance calculation. Use of VIF could increase the 

retention of methyl iodide and amount of iodide in the soil, causing higher groundwater 

concentrations than estimated in the risk assessment. Any groundwater contamination would take 

years to occur. An adequate field dissipation study would provide data to better estimate 
John S. Sanders, Ph.D. 

April 29, 2010 

Page 8 

groundwater concentrations, followed by mitigation measures if needed. Alternatively, 

mitigation measures could be implemented immediately. Mitigation measures should include 

buffer zones around wellheads, and irrigation restrictions in ground water protection areas. 
Page 9

Attachment 1–Estimated Buffer Zone Distances 

Methyl iodide buffer zone distances (feet) for 32 ppb, 24-hour exposure. 

Buffers calculated using PERFUM model and Ventura weather data. 

Buffers longer than 4723 feet (1440 meters) estimated by extrapolation. 

Distances represent the 95th percentile in the maximum direction. 

Broadcast-shallow shank fumigation method. 

Flux is average of Manteca and Watsonville studies (43% of applied amount for peak 24 hrs). 

Table 1-1. Broadcast-shallow shank method with standard tarp 

Broadcast app Buffer Zone (feet) for Various Field Sizes 

rate (lbs MeI/acre) 1 acre 5 acres 10 acres 20 acres 30 acres 40 acres

51 67 296 480 793 1,034 1,269

75 162 532 841 1,318 1,665 2,055

100 236 734 1,154 1,788 2,241 2,770

125 319 937 1,464 2,239 2,782 3,443

176 462 1,306 2,031 3,075 3,795 4,704

Table 1-2. Broadcast-shallow shank with VIF (30% flux reduction) 

Broadcast app Buffer Zone (feet) for Various Field Sizes 

rate (lbs MeI/acre) 1 acre 5 acres 10 acres 20 acres 30 acres 40 acres

50 14 162 274 489 666 811

75 92 360 578 937 1,207 1,485

100 166 546 863 1,352 1,707 2,107

125 227 705 1,108 1,717 2,151 2,659

175 343 1,009 1,577 2,411 2,995 3,708

Table 1-3. Broadcast-shallow shank with VIF (40% flux reduction) 

Broadcast app Buffer Zone (feet) for Various Field Sizes 

rate (lbs MeI/acre) 1 acre 5 acres 10 acres 20 acres 30 acres 40 acres

50 13 150 255 455 619 754

75 70 310 503 830 1,082 1,328

100 129 470 750 1,201 1,535 1,891

125 211 656 1,031 1,597 2,001 2,473

175 319 937 1,464 2,239 2,782 3,443

Table 1-4. Broadcast-shallow shank with VIF (50% flux reduction) 

Broadcast app Buffer Zone (feet) for Various Field Sizes 

rate (lbs MeI/acre) 1 acre 5 acres 10 acres 20 acres 30 acres 40 acres

50 12 93 170 340 489 590

75 65 289 469 774 1,009 1,239

100 121 439 700 1,120 1,433 1,765

125 180 591 934 1,465 1,849 2,283

175 289 870 1,363 2,095 2,612 3,232
Page 10 

Methyl iodide buffer zone distances (feet) for 32 ppb, 24-hour exposure. 

Buffers calculated using PERFUM model and Ventura weather data. 

Buffers longer than 4723 feet (1440 meters) estimated by extrapolation. 

Distances represent the 95th percentile in the maximum direction. 

Bed-shallow shank fumigation method. 

Flux is average of Guadalupe and Oxnard studies (57% of applied amount for peak 24 hrs). 

Table 1-5. Bed-shallow shank method with standard tarp 

Broadcast app rate Buffer Zone (feet) for Various Field Sizes 

(lbs MeI/acre) 1 acre 5 acres 10 acres 20 acres 30 acres 40 acres

50 157 588 965 1,507 2,273 2,418

75 300 951 1,502 2,198 3,315 3,527

100 417 1,275 1,993 2,865 4,321 4,597

125 538 1,575 2,432 3,422 5,160 5,489

176 754 2,140 3,274 4,528 6,827 7,262

Table 1-6. Bed-shallow shank with VIF (30% flux reduction) 

Broadcast app rate Buffer Zone (feet) for Various Field Sizes 

(lbs MeI/acre) 1 acre 5 acres 10 acres 20 acres 30 acres 40 acres

50 81 397 684 1,145 1,728 1,839

75 198 698 1,132 1,731 2,611 2,778

100 308 976 1,541 2,254 3,400 3,617

125 401 1,224 1,913 2,751 4,148 4,413

175 579 1,696 2,619 3,685 5,557 5,911

Table 1-7. Bed-shallow shank with VIF (40% flux reduction) 

Broadcast app rate Buffer Zone (feet) for Various Field Sizes 

(lbs MeI/acre) 1 acre 5 acres 10 acres 20 acres 30 acres 40 acres

50 76 369 636 1,065 1,607 1,710

75 168 630 1,034 1,614 2,435 2,591

100 261 884 1,419 2,134 3,219 3,425

125 357 1,133 1,788 2,617 3,946 4,198

175 538 1,575 2,432 3,422 5,160 5,489

Table 1-8. Bed-shallow shank with VIF (50% flux reduction) 

Broadcast app rate Buffer Zone (feet) for Various Field Sizes 

(lbs MeI/acre) 1 acre 5 acres 10 acres 20 acres 30 acres 40 acres

50 41 299 543 971 1,466 1,560

75 157 588 965 1,507 2,273 2,418

100 244 825 1,324 1,992 3,005 3,197

125 333 1,057 1,669 2,442 3,683 3,919

175 497 1,482 2,301 3,267 4,926 5,240
Page 11 

Methyl iodide buffer zone distances (feet) for 32 ppb, 24-hour exposure. 

Buffers calculated using PERFUM model and Ventura weather data. 

Buffers longer than 4723 feet (1440 meters) estimated by extrapolation. 

Distances represent the 95th percentile in the maximum direction. 

Drip fumigation method. 

Flux is average of Camarillo, La Selva, Guadalupe studies (54% of applied amount for 24 hrs). 

Table 1-9. Drip with standard tarp 

Broadcast app rate Buffer Zone (feet) for Various Field Sizes 

(lbs MeI/acre) 1 acre 5 acres 10 acres 20 acres 30 acres 40 acres

51 47 175 340 530 707 878

75 116 346 588 911 1,173 1,451

100 170 486 805 1,245 1,591 1,966

125 230 634 1,018 1,572 1,991 2,457

176 334 896 1,409 2,174 2,734 3,371

Table 1-10. Drip with VIF (30% flux reduction) 

Broadcast app rate Buffer Zone (feet) for Various Field Sizes 

(lbs MeI/acre) 1 acre 5 acres 10 acres 20 acres 30 acres 40 acres

50 9 79 198 311 437 546

75 65 221 408 634 834 1,035

100 119 355 603 934 1,203 1,488

125 163 467 773 1,195 1,527 1,887

175 248 682 1,097 1,693 2,144 2,646

Table 1-11. Drip with VIF (40% flux reduction) 

Broadcast app rate Buffer Zone (feet) for Various Field Sizes 

(lbs MeI/acre) 1 acre 5 acres 10 acres 20 acres 30 acres 40 acres

50 8 74 184 289 406 508

75 49 184 356 555 740 919

100 92 295 528 819 1,069 1,325

125 152 434 719 1,112 1,420 1,755

175 230 634 1,018 1,572 1,991 2,457

Table 1-12. Drip with VIF (50% flux reduction) 

Broadcast app rate Buffer Zone (feet) for Various Field Sizes 

(lbs MeI/acre) 1 acre 5 acres 10 acres 20 acres 30 acres 40 acres

50 7 29 127 202 305 384

75 46 171 332 518 690 858

100 86 276 492 764 998 1,236

125 129 384 654 1,012 1,304 1,612

175 192 538 875 1,351 1,717 2,120