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<br />State Water Resources Control Board <br />Division of Water Quality <br />1001 I Street, Sacramento, California 95814* (916) 341-5455 <br />Mailing Address: P.O. Box 2231, Sacramento, California 95812 <br />Fax (916) 341-5808 • Internet Address: http://www.waterboards.ca.gov <br /> <br />Linda S. Adams <br />Secretaiy for <br />Environmental Protection <br /> <br />Arnold Schwarzenegger <br />Governor <br /> <br />AUG 3 1 2010 <br />To: Underground Storage Tank Local Regulatory Agencies and Interested Persons <br />REGULATORY STATUS OF UNDERGROUND STORAGE TANKS STORING <br />AQUEOUS UREA SOLUTION <br />The State Water Resources Control Board (State Water Board) is providing guidance <br />on the regulatory status of underground storage tanks (USTs) storing aqueous urea, <br />which is commonly referred to as diesel exhaust fluid or DEF. <br />DEF is approximately 30 percent aqueous solution of urea used in Selective Catalytic <br />Reduction technology and may contain a small amount of ammonia. As explained in <br />the United States Environmental Protection Agency's (EPA)'s letter dated <br />September 22, 2009, a copy of which is enclosed, the international standard for DEF <br />allows no more than 0.2 percent by weight of alkalinity, measured as ammonia, to be <br />present in the solution. Manufacturers indicate, however, that the actual amount of <br />ammonia in the solution should be much less than 0.2 percent, and ideally there should <br />be no ammonia in the solution. The EPA has determined that USTs storing DEF are <br />not regulated under the federal act. (See September 22, 2009 letter from EPA.) <br />The State Water Board has determined that DEF, with an approximate urea solution of <br />30 percent, is not a hazardous substance as defined in Section 25281 of the Health and <br />Safety Code and, accordingly, USTs storing DEF are not regulated under Chapter 6.7 of <br />the Health and Safety Code. <br />If you have any questions about this matter, please contact Ms. Laura Fisher at <br />(916) 341-5780 or via email at Ifisherwaterboards.ca.qov. <br />Kevin L. Graves, Manager <br />Underground Storage Tank Program <br />California Environmental Protection Agency <br />(.5' Recycled Paper