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7080.2230 INDIVIDUAL SUBSURFACE SEWAGE TREATMENT SYSTEMS 52 <br />T. Construction vehicles must not be allowed on the distribution media until backfill is placed <br />as described in item S. <br />U. A minimum of six inches of topsoil borrow must be placed over the entire mound. <br />Statutory Authority: MS s 115.03; 115.55 <br />History: 32 SR 1347; 35 SR 1353 <br />Published Electronically: October 10, 2013 <br />7080.2230 AT -GRADE SYSTEMS. <br />Subpart 1. At -grade system. To qualify as an at -grade system, the system must meet or exceed the <br />following requirements: <br />A. employ flow values in parts 7080.1850 to 7080.1885; <br />B. meet or exceed applicable technical requirements of parts 7080.1900 to 7080.2030, <br />7080.2050, and 7080.2100; <br />C. meet or exceed the requirements of part 7080.2150, subparts 2 and 3; <br />D. employ flow measurement; and <br />E. meet the requirements of subparts 2 and 3. <br />Subp. 2. Location of at -grade systems. <br />A. The upper 12 inches of the absorption area must be original soil with a loading rate of 0.45 <br />gallons per day per square foot or greater as shown in Table IX or 1Xa in part 7080.2150, subpart 3, item E. <br />B. At -grade systems must not be installed in areas with slopes greater than 25 percent. <br />C. Setbacks must be according to part 7080.2150, subpart 2, item F. Setbacks must be measured <br />from the absorption area. <br />Subp. 3. Design and construction of at -grade systems. <br />A. The at -grade bed absorption width must be determined according to part 7080.2150, subpart <br />3, item M, and must not exceed a width of 15 feet. The at -grade bed absorption width for slopes of one <br />percent or greater does not include any width of the media necessary to support the upslope side of the pipe. <br />B. The at -grade absorption length must be calculated by dividing the design flow by the soil <br />loading rate found in Table IX or 1Xa in part 7080.2150, subpart 3, item E, for the upper 12 inches of soil <br />and dividing by the absorption bed width. <br />C. At -grade systems must employ pressurized distribution by meeting or exceeding the <br />applicable requirements of parts 7080.2050 and 7080.2100. At -grade systems located on slopes of one <br />percent or greater require only one distribution pipe located on the upslope edge of the distribution media, <br />with the absorption bed width being measured from the distribution pipe to the downslope edge of the <br />media. Multiple distribution pipes are allowed to be used to provide even distribution, if necessary, based <br />on site conditions. <br />compaction. <br />D. The upslope edge of an at -grade absorption bed must be installed along the natural contour. <br />E. At -grade materials must be placed by using construction techniques that minimize <br />Copyright ©2014 by the Rev <br />so <br />of Statutes, State of Minnesota. All Rights Reserved. <br />