Calculating Buffer Zones: A Guide for Applicators
This page will help fumigant applicators understand how to calculate required sizes of buffer zones and learn ways to reduce sizes of buffer zones.
Metam Sodium – Shank Injection – Broadcast
What are Buffer Zones?
Buffer zones provide distance between the application block (i.e., edge of the treated field) and bystanders. Buffer zones:
- Allow airborne residues to disperse before reaching bystanders, reducing the potential for fumigant exposure.
- Are established around the perimeter of the application block.
- Extend outward from the edge of the application block perimeter equally in all directions
|Buffer Zone →||
For more information on buffer zones, see the EPA’s fact sheets on Buffer Zones and Posting Requirements for Buffer Zones.
How to Use Look-Up Tables to Determine a Buffer Zone
Soil fumigant product labels provide look-up tables that a certified applicator will use to determine the buffer zone. The buffer zone distance will be determined by the broadcast equivalent application rate and the size of the application block. The broadcast equivalent rate is the application rate for the fumigant applied to the entire application block, based on the:
- amount of fumigant applied in beds/strips; and
- size of untreated areas.
See the product label for instructions on calculating the broadcast equivalent rate.
When using the tables, round up to the nearest rate and block size, if applicable. Applications are prohibited for rates and block sizes that exceed what is presented in the buffer zone tables.
Examples of Look-up Tables
Buffer Zone Distance Requirements
- 25 feet is the minimum buffer zone distance, regardless of credits or site-specific application parameters
- The application is prohibited if the buffer zone is greater than ½ mile (2,640 feet)
Example 1 - Basic Use of Look-Up Table
|Application Block Size (acres)|
The table above is an example of a look-up table. Use the table from the label that is specific to the application method. Using the example table above, if an applicator applies metam sodium by shank injection to beds at the broadcast equivalent rate of 75 gallons per acre (gal/acre) to an application block that is 120 acres, the buffer zone is 129 feet.
Example 2 - Rounding Up When Using Look-Up Table
Using the same table, if the applicator is making the same application but at a broadcast equivalent rate of 80 gal/acre, you must round up to the next application rate – in this case, 85 gal/acre. The buffer zone for this scenario is 153 feet.
How to Use Credits to Calculate a Buffer Zone
Depending on the fumigant, credits that are listed on product labels can be used to reduce the buffer zone by up to 80 percent. Reminder: The minimum buffer zone distance is 25 feet regardless of buffer zone credits.
The credits that are listed on product labels are fumigant-specific but can be based on factors that reduce fumigant off-gassing such as:
- Use of specific high-barrier tarps (see Tarps).
- Use of potassium thiosulfate.
- Organic content of the soil.
- Clay content of the soil.
- Soil temperature.
- Water seals.
- Symmetry™ application system.
Keep in mind that the types of credits allowed are product-specific. Always check the label to see which credits may be applicable.
To use a buffer zone credit, use the formula below to calculate the size of the reduced buffer zone:
Size of buffer zone – (size of buffer zone x % credit) = Size of reduced buffer zone
Example 1 - Basic Credit Reduction
|Application Block Size (acres)|
An applicator wants to apply 75 gal/acre to 100 acres. Using the table above, we see that the buffer zone distance is 98 feet.
The applicator is applying to soil that has 2.5% organic matter, for which the product label allows a 20% credit to reduce the buffer zone. To calculate the reduced buffer zone, use the formula above:
- 98 - (98 x 20%) = Size of reduced buffer zone
- 98 - (19.6) = 78.4 feet
EPA expects that applicators will round to the nearest whole number. In cases where the decimal is .5 or above, the applicator should round up. In this case, the applicator would round down to 78 feet.
Example 2 - Multiple Credit Reductions
In some cases, there may be multiple credits that can be used. For example, an applicator may be able to use the following credits listed on a product label:
- Applies to a field with 2.5% organic matter = 20% credit
- Applies to a field where the soil temperature is less than 50ºF = 10% credit
- Applies to a field where the clay content is greater than 27% = 10% credit
Note that the credits, in this case, cannot exceed 80%.
Using the same scenario above, we can calculate what the buffer zone will be with the multiple credits. First, you need to add the credits together.
20% organic matter credit + 10% soil temperature credit + 10% clay content credit = 40% credit
Then, using the same formula as above:
- 98 - (98 x 40%) = Size of reduced buffer zone
- 98 - 39.2 = 58.8 feet
In this case, the applicator should round up to 59 feet.
Other Ways to Reduce Buffer Zones
There are other ways, besides using buffer zone credits, to reduce the size of buffer zone. Some examples:
- Use a lower application rate.
- Divide the application block into smaller application block sizes.
- Use a different application method.
Example 1 - Use a Lower Application Rate
|Application Block Size (acres)|
An applicator is making an application to a 120-acre application block. The applicator has determined that an application rate of 75 - 85 gal/acre will be effective. Using the table above, the applicator sees that the buffer zone is 153 feet with the 85 gal/acre application rate and 129 feet with the 75 gal/acre application rate. Using 75 gal/acre will result in a buffer zone that is 24 feet smaller than if the higher rate is used.
Example 2 - Divide the Application Block
The applicator chooses to use the 75 gal/acre application rate and still needs to apply the product to 120 acres but would like to further reduce the buffer zone. The applicator decides to divide the application block in half. Using the table above, the buffer zone for each 60 acre application block is 72 feet, significantly reducing the buffer zone for each application block.
Follow the label directions for applications regarding buffer zone proximity. For overlapping buffer zones, a minimum amount of time must elapse for most application methods before the second application can occur.
Example 3 - Using Application Parameters and Credits in Combination to Reduce Buffer Zones
The applicator is pleased to have reduced the buffer zone to 72 feet but checks to see if it is possible to use any buffer zone credits.
The applicator notes that the soil has 2.5% organic matter, for which the label allows a 20% credit to reduce the buffer zone. The applicator calculates the reduced buffer zone:
- 72 - (72 x 20%) = Size of reduced buffer zone
- 72 - (14.4) = 57.6 feet
The size of the buffer zone should be rounded up to 58 feet.
Using a combination of modifying the application parameters and applying credits, the applicator ends up with a buffer zone of 58 feet.
Buffer Zone Calculator
This tool, developed by EPA, is specific to each fumigant product and is based on the look-up tables on the product labels. In addition to calculating buffer zone distances, the calculator can also be used to quickly calculate buffer zone reductions through the use of credits and modifications to application parameters. Applicators must verify that the buffer zone results from the calculator are consistent with the buffer zone requirements on product labels. If there are any discrepancies, the label must be followed.
Use the Buffer Zone Calculator