Office of Air Quality, Permitting & Enforcement Division Mechanical Section Policy Memorandum þÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ Date: February 17, 1994 No.: 10 From: Skip Clark, P.e. Approved by: Gary I. Wallin, P.E. Subject: Standard Exemption Nos. 77 and 114 þÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ Policy: Both exemptions cover sand and gravel production facilities. Standard Exemption No. 77 is to be used when the sand and gravel is mined from subterranean and subaqueous beds, or in other words, the material is mined wet naturally. Standard Exemption No. 114 is to be used when the sand and gravel is mined dry. In both cases, no crushing is allowed, but classification can be done. In both cases, in-plant roads can be either sprinkled with water and/or chemicals or paved and cleaned. Background: These exemptions were developed for mining naturally occurring deposits of sand and gravel. Since the subterranean and subaqueous beds are wet to begin with, the allowed production rate is 500 tons per hour. Additional watering of the process and/or stockpiles is permitted, along with the required sprinkling of the in-plant roads (unless paved). For the deposits that are dry, usually this means surface mining, the production rate is limited to fifty tons per hour. Water sprays are required on screens, transfer points, stockpiles, in-plant roads (unless paved) and where necessary. Again, no crushing is allowed in either exemption. Necessary Action: The exemptions need to have the wording concerning the in-plant roads clarified to reflect the intent that they can be either paved and cleaned or sprinkled with water and/or chemicals as necessary to achieve maximum control of dust emissions. cc: All Mechanical Section