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t CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD CENTRAL VALLEY REGION Fact Sheet No. 1 For Dairies `Does Yo-urbairy Nee&An NPDES Stormwatef.'Permit?°' Federal law and regulations require that certain dairies have a National Pollutant Discharge Elimination System (NPDES) permit issued under the federal Clean Water Act. This fact sheet provides information to help you determine.if your dairy trust have an NPDES stormwater permit. In the discussion below, an "Animal Unit" (AU) is-1,000 pounds of animal(s), and "surface water" is a water of the state. Fo' Question: What are the typical surface water quality problems associated with a dairy? Answer Wastewater from a dairy is high in nitrogen, ammonia, salts,-and organic material (manure and other solids). When nitrogen and ammonia are discharged.to a creek or stream, they can be Fit' poisonous to the plants and animals living in the waters. Organic material can reduce or remove the dissolved oxygen in a creek or stream, thereby suffocating the fish that live there. In addition, manure, like any other waste produced by warm-blooded.animals, contains bacteria that could pose a threat to human health and/or sources of drinking water. Any of these pollutants, if discharged from a sewage treatment plant to surface water, would be regulated by an NPDES pen-nit. t Question, When does a dairy need an NPDES stormwater permit? Answer: A dairy is required to have an NPDES stormwater permit if it has the potential to discharge to surface water, and: 1. the dairy has over 1,000 AU(more than 700 or more mills and/or dry cows)confined or corralled for 45 _ or more days during any i2 months period,or 2. the dairy has 301 to L,000 AU(200 to 700 milk and dry cows)and animal waste was discharged to 4 Y surface.water through a man-made conveyance(ditch,pipe,etc.),or was discharged into a surface water drainage course passing through the dairy (originating and ending outside the dairy), or 3. the dairy has been designated as a concentrated animal feeding operation(CAFO)by the Regional Water F Quality Control Board(Regional Board) as a potential or actual significant contributor to pollution of surface waters. F", Question: Can a dairy be exempt from obtaining an NPDES stormwater permit? Answer: Regardless of herd size, a dairy does not need an NPDES stormwater permit if it is managed .such that discharges to surface water occur only during storm events greater than the 25-year 24-hour storm event. (The 25-year 24-hour storm event is rainfall in a 24-hour period expected to occur once every 25 years.) ' Question: How does a dairy operator determine the size of the 25 year 24-hour storm? Answer: The National Oceanic and Air Administrator of the National Weather Servile has detennined the water amounts in a 25-year 24-hour storm. For example, in the San Joaquin Valley, the 25-year 24-hour storm will generate about 2.5 inches of rain. Contact your local weather .. service or the local office of the National Resources Conservation Service to obtain actual-.- rainfall values for your area. County building and road departments also often have this information.