These manure application setback guidelines were developed for Western Washington to help prevent runoff events associated with manure application. However, these guidelines can also be followed during rain and/or irrigation events in Eastern Washington to prevent runoff events. Setback distances are based on historical weather data and scientific studies which recommend specific distances for sediment and nutrient removal based on seasonal precipitation and soil saturation conditions.
Manure application setback distances should be used year round to help prevent a runoff event from your field to a nearby waterbody or critical area. Additional static setbacks may be required near wells, fence lines, or other identified areas.
Setbacks can be used alone or in conjunction with a vegetative buffer, if necessary, to achieve the level or resource protection desired. When used properly, setbacks can help prevent overland flow of manure caused by precipitation or irrigation water. However, it must be noted that they alone will not prevent a manure runoff event. Good management and proper field conditions must be observed in addition.
When applying manure, remember to follow guidance posted on the Manure Spreading Advisory. These setbacks will help you avoid applying too close to a waterbody or sensitive area when the risk of runoff is high. Your Nutrient Management Plan requires the implementation of these setbacks.
A distance of 40 feet has been shown to be most effectual under Western WA spring and fall rain events at preventing runoff of surface nutrients and sediment. That distance is reduced to 10 feet in the dry summer months when the chance of runoff is slight due to low precipitation. In the face of a summer rain event, however, setback distances should be increased to 40+ feet. During the late fall to winter months, the setback distance is increased to 80 feet to be protective against periods of heavy, prolonged rain events, and/or saturated soils, which require greater distances for nutrients and pathogens to be removed/treated prior to reaching a waterway.
For further information on setback distances and vegetative buffer guidelines, review the following non-peer reviewed paper: Ideal Vegetative Conservation Practice Implementation for Prevention of Runoff from Manure Applied Fields (PDF)
If you have any discharge due to poor management, you may be put under the penalty of an EPA CAFO permit with a mandatory setback of 100 feet year-round.