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INDUSTRY, LABOR AND HUMAN RELATIONS 39 <br /> Ind 8 <br /> 3. The route of the drainage system shall be so located that, if the <br /> liquids in the drainage system are ignited, the fire will not seriously <br /> expose tanks or adjoining property;and <br /> 4.The confines of the impounding area shall be located so that when <br /> filled to capacity the liquid level will not be closer than 50 feet from any <br /> property line that is or can be built upon,or from any tank. <br /> (c) [2-2.3.3] Impounding around tanks by diking. When protection <br /> of adjoining property or waterways is by means of impounding by diking <br /> around the tanks,such system shall comply with the following: <br /> 1. A slope of not less than 1 percent away from the tank shall be <br /> provided for at least 50 feet or to the dike base,whichever is less; <br /> • 2.The volumetric capacity of the diked area shall not be less than the <br /> greatest amount of liquid that can be released from the largest tank <br /> within the diked area, assuming a full tank. To allow for volume <br /> occupied by tanks, the capacity of the diked area enclosing more than <br /> one tank shall be calculated after deducting the volume of the tanks, <br /> other than the largest tank, below the height of the dike; <br /> 3.To permit access, the outside base of the dike at ground level shall <br /> be no closer than 10 feet to any property line that is or can be built upon; <br /> 4. Walls of the diked area shall be of earth, steel, concrete or solid <br /> masonry designed to be liquid-tight and to withstand a full hydrostatic <br /> head. Earthen walls 3 feet or more in height shall have a flat section at <br /> the top of not less than 2 feet wide.The slope of an earthen wall shall be <br /> consistent with the angle of repose of the material of which the wall is <br /> constructed. Diked areas for tanks containing Class I liquids located in <br /> extremely porous soils shall require special treatment to prevent <br /> seepage of hazardous quantities of liquids to low-lying areas or <br /> waterways in case of spills; <br /> 5.Except as provided in subd.6.a.,the walls of the diked area shall be <br /> restricted,to an average interior height of 6 feet above interior grade; <br /> 6. Dikes may be higher than an average of 6 feet above interior grade <br /> where provisions are made for normal access and necessary emergency <br /> access to tanks, valves and other equipment, and safe egress from the <br /> diked enclosure; <br /> a. Where the average height of the dike containing Class I liquids is <br /> over 12 feet high, measured from interior grade, or where the distance <br /> between any tank and the top inside edge of the dike wall is less than the <br /> • height of the dike wall,provisions shall be made for normal operation of <br /> • valves and for access to tank roof without entering below the top of the <br /> dike. These provisions may be met through the use of remote operated <br /> valves, elevated walkways or similar arrangements. <br /> b. Piping passing through dike walls shall be designed to prevent <br /> excessive stresses as a result of settlement or fire exposure. <br /> c. The minimum distance between tanks and toe of the interior dike <br /> walls shall be 5 feet. <br /> 7. Each diked area containing 2 or more tanks shall be subdivided <br /> preferably by drainage channels or at least by intermediate curbs in <br /> Register,March, 1982,No.315 <br />