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47 INDIVIDUAL SUBSURFACE SEWAGE TREATMENT SYSTEMS 7080.2150 61 to 120 - 5.0 0.3 5.3 >120 F. If drainfield rock medium is employed, a durable, nonwoven geotextile fabric must be used to cover the distribution rock medium. The fabric must be of sufficient strength to undergo installation without rupture. The fabric must permit passage of water without passage of overlying soil material into the rock medium. G. All excavation into the absorption area, or surface preparation of the upper 12 inches of absorption area, must be in a manner to expose the original soil structure in an unsmeared and uncompacted condition. Excavation is only allowed when the soil moisture content is at or less than the plastic limit and is not frozen or freezing. H. Excavation equipment or other vehicles must not be driven on the excavated or prepared absorption area. Foot traffic on these areas must be minimized and not cause compaction. The exposed areas must be immediately covered with media or the designed coverage materials. If the areas are exposed to direct rainfall, they must be allowed to dry and must be re -prepared according to item G. I. A minimum of six inches of topsoil borrow must be placed over the system. J. A close -growing, vigorous vegetative cover must be established over the soil treatment and dispersal system and other vegetatively disturbed areas. The sodding, seeding, or other vegetation establishment must begin immediately after the placement of the topsoil borrow. If the climatic season does not allow immediate establishment of vegetation, the soil treatment and dispersal system must be protected from erosion and excessive frost and a vegetative cover must be established as soon as favorable climatic conditions exist. The vegetative cover established must not interfere with the hydraulic performance of the system and must provide adequate frost and erosion protection. Trees, shrubs, deep-rooted plants, or hydrophytic plants must not be planted on the system. K. Sewage tank effluent concentrations to the soil dispersal system must not exceed a BOD concentration of 170 mg/1, a CBOD5 concentration of 125 mg/1, a TSS concentration of 60 mg/1, or an oil and grease concentration of 25 mg/l. L. The distribution media must not be in contact with soils with any of the USDA soil textures classified as sand with 35 percent or more rock fragments or loamy sand with 35 percent or more rock fragments or any soils that have a percolation rate of less than 0.1 minute per inch. M. The contour loading rate for soil dispersal systems must be between 1 and 12 gallons per lineal foot per day. Subp. 4. Systems with a design flow greater than 2,500 gallons per day. At a minimum, systems designed under this chapter with a design flow of greater than 2,500 gallons per day, which impact water quality of an aquifer, as defined in part 4725.0100, subpart 21, must employ best management practices for nitrogen reduction developed by the commissioner to mitigate water quality impacts to groundwater. Statutory Authority: MS s 115.03; 115.55 History: 32 SR 1347; 35 SR 1353; 38 SR 1001 Published Electronically: January 22, 2014 Copyright ©2014 by the Rev so of Statutes, State of Minnesota. All Rights Reserved.