Project Number: 0500-00044-021-08
Project Type: Specific Cooperative Agreement

Start Date: Sep 25, 2008
End Date: Jun 30, 2009

Objective:
1) Evaluate VIF sealing practices vs. standard PE tarp with and without thiosulfate chemical seal for reduction of fumigant off-gassing; 2) Evaluate deep shank injection with thiosulfate seal for reduction of fumigant off-gassing; and 3) Implement a stakeholder outreach plan when results are available to promote the use of alternative methods to improve product efficacy and encourage sound environmental management of fumigants.

Approach:
This study will be conducted in the Ventura County on four adjacent fields. Each field will be one or two acres, and the four fields will be separated from each other by >1000 ft to avoid cross contamination. The fields will contain the same soil type, soil moisture, and prepared following standard field preparation practices by cooperating growers. The sealing treatments will be: 1) standard polyethylene (PE) tarp, 2) VIF, 3) VIF/thiosulfate chemical seal, and 4) deep shank injection plus thiosulfate/water seal. Thiosulfate will be sprayed on the soil surface immediately before tarping to help degrade chloropicrin trapped between the soil surface and VIF. A sprinkler system will be installed on one field (deep shank injection treatment) and 6 mm of water containing 25 gal/A thiosulfate will be applied to seal the soil immediately after shank injection. Chloropicrin will be shank-applied in fields (treatments) 1, 2, and 3 at 12 inches and in field (treatment) 4 at 18 inches. In all fields, chloropicrin application rate will be 300 lbs/ac. After application, chloropicrin will be monitored for 14 days using XAD resin. We will work with local fumigators and the Agricultural Commissioner¿s office to ensure that no other Pic application is taking place in the proximity of the test fields during the monitoring period. Emission rates will be determined for each field using the off-site indirect method. This indirect flux method is the most widely used and accepted method. This method uses the Industrial Source Complex Short Term (ISCST3) model and an atmospheric dispersion model used by EPA for regulatory purposes. The ISCST3 and/or CALPUFF 6.0 air dispersion models will be used in the emissions analysis. The ambient monitoring-based air concentration data and the normalized modeled data based on an emission rate of 1 ug/m2/sec for each of the 4 hour periods and the meteorological data will be used to calculate the emission rates. Measured air quality concentrations will be scaled up to account for average measured recovery efficiency. Standard regression between the measured and modeled dataset for a period will be performed. If the slope is significant and the intercept term is not significant, the emission rate will be based on the regression slope value. Otherwise, the least squares slope method (regression without an intercept term) will be used to estimate the emission rate. If the slope using that method is not significant, then other methods are required such as averaging the measured values and dividing that number by the average of the modeled values, diurnal matching, or interpolation between periods. Standard errors of the mean emission rate calculated by the regression will be computed from the residuals of each fitting period, and distributions established to identify the uncertainty in the results. Documents SCA with UC Davis.