(A) Systems designed according to this section are considered Type I Systems. Systems in soils with a loading rate less than 0.45 gallons per day per square foot cannot be used in a Type I system for new construction.
(B) Trenches and seepage beds.
(1) To qualify as a trench or seepage bed system, the system must meet or exceed the following requirements:
(a) Employ flow values in § 52.12.
(c) Meet or exceed the requirements of § 52.16(B) and (C).
(d) Meet the requirements of divisions (B) to (O) of this section.
(2) Seepage bed placement must be limited to areas having natural slopes of less than 6%. Absorption areas for seepage beds must not be placed in soils with a texture group of 8 on Table IX in Minn. Rule 7080.21501. Seepage beds must not be located in floodplains.
(3) The trench bottom absorption area is calculated by dividing the design flow by the appropriate sol loading rate in Table IX in Minn. Rule 7080.21501 or Table VI.
(4) If gravity distribution is used in seepage beds, the seepage bed absorption area is calculated by dividing the design flow by the soil loading rate and then multiplying that value by 1.5.
(5) If pressure distribution is used in seepage beds, the seepage bed absorption area is determined by dividing the design flow by the soil loading rate in Table IX in Minn. Rule 7080.21501 or Table VI.
(6) The minimum sidewall absorption is six inches. The bottom absorption area is allowed to be reduced, for gravity distribution trenches only, by the following:
Sidewall Absorption - Inches | Sizing Equivalent |
8-11 | 7% |
12-17 | 20% |
18-23 | 34% |
24 | 40% |
(7) Trenches must be no more than 36 inches wide. Any excavation wider than 36 inches shall be considered a seepage bed.
(8) A seepage bed must not be wider than 12 feet if gravity distribution is used.
(9) A seepage bed must not be wider than 25 feet if pressure distribution is used.
(10) Natural, undisturbed soil must exist between multiple trenches and seepage beds.
(12) A vertical inspection pipe at least four inches in diameter must be installed and secured in the distribution medium of every trench and seepage bed. The inspection pipe must be located at an end opposite from where the sewage tank effluent enters the medium. The inspection pipe must have three-eighths inch or larger perforations spaced vertically no more than six inches apart. At least two perforations must be located in the distribution medium. Perforations must not be located above the geotextile cover or wrap. The inspection pipe must extend to the bottom of the distribution medium, be secured, and be capped flush with or above finished grade.
(13) The top and bottom of the distribution medium must be level along the contour. Sidewalls must be as vertical as practical and not intentionally sloped.
(14) The minimum depth of soil cover, including topsoil borrow, over the distribution medium is 12 inches.
(15) Trenches or seepage beds must be backfilled and crowned above finished grade to allow for settling. The top six inches of the backfill must have the same texture as the adjacent soil.
(C) Mounds.
(1) To qualify as a mound system, the system must meet or exceed the following requirements:
(a) Employ flow values in § 52.12.
(c) Meet or exceed the requirements of § 52.16.(B)2 and (C).
(D) Meet the requirements of § 52.17(C)(2) to(C) (30).
Location of mounds.
(2) The upper 18 inches of the original soil mound absorption area must have a minimum loading rate of 0.45 gallons per day per square foot and a mound absorption ratio greater than zero, but no more than 2.6 in Table IX in Minn. Rules 7080.21501 or Table VI. The upper 18 inches of the absorption area must also be above the periodically saturated soil or bedrock.
(3) For previously developed sites, the upper 12 inches of the original soil mound absorption area must have a mound absorption ratio of greater than zero in Table IX in Minn. Rules 7080.21501 or Table VI. The upper 12 inches of the absorption area must also be above the periodically saturated soil or bedrock.
(4) Setbacks must be according to Table V. Setbacks must be measured from the original soil absorption area.
(5) On slopes of one percent or greater and where the original soil mound absorption ratio is 2.6 or greater in Table IX in Minn. Rules 7080.21501 or Table VI, mounds must not be located where the ground surface contour lines that lie directly below the long axis of the distribution media bed represent a swale or draw, unless the contour lines have a radius of curvature greater than 100 feet. In no case shall mounds be placed on slopes greater than 12%.
(6) Mounds must never be located in swales or draws where the radius of curvature of the contour line is less than 50 feet.
Mound design and construction.
(7) The mound distribution media bed area consists of bottom area only and must be calculated by dividing the design flow by 1.0 gallons per square foot per day.
(8) The mound distribution media bed area must be as long and narrow as practical. Mound distribution media beds must be no wider than ten feet.
(9) Mound distribution bed length and width must be determined by the contour loading rate, which is the relationship between the vertical and horizontal water movement based on the following soil conditions:
(a) The permeability difference between the original soil mound absorption area and slower permeability horizons below the original soil mound absorption area.
(b) The depth between the original soil mound absorption area and the change in permeability described in division (a) above.
(c) The land slope.
(10) Clean sand must be used to elevate the mound distribution media bed and must consist of sound, durable material that conforms to the following requirements:
Sieve Size | Percent Passing |
No. 4 | 95-100 |
No. 8 | 80-100 |
No. 10 | 0-100 |
No. 40 | 0-100 |
No. 60 | 0-40 |
No. 200 | 0-5 |
Clean sand must also contain less than three percent deleterious substances and be free of organic impurities.
(11) The original soil mound absorption area is determined by multiplying the original soil mound absorption length by the original soil mound absorption width. The original soil absorption width calculated by multiplying the mound distribution media bed width by the mound absorption ratio. The mound absorption ratio of the upper 18 inches of soil for new construction, or 12 inches of so: for previously developed sites, in the proposed original soil mound absorption area shall be determined according to Table IX in Minn. Rule 7080.21501 or Table VI.
(12) The required original soil absorption width for mounds constructed on slopes from zero to one percent must be centered under the mound distribution media bed width. The required original mound soil absorption width constructed on slopes greater than one percent must be measured downslope from the upslope edge of the mound distribution media bed width and measured in the direction of the original land slope and perpendicular to the original contours.
(13) The side slopes on the mound must no be steeper than three horizontal units to one vertical unit and shall extend beyond the required absorption area, if necessary.
(15) The supply pipe from the pump to the original soil absorption area must be installed before surface preparation of the original mound soil absorption area. The trench excavated for the supply pipe must be carefully backfilled and compacted to prevent seepage of effluent.
(16) Vegetation in excess of two inches in length and dead organic debris including leaf mats must be removed from the original soil mound absorption area. Trees must be cut nearly flush with the ground and stumps must not be removed.
(17) The original soil mound absorption area must be roughened by backhoe teeth, moldboard, or chisel plow. The soil must be roughened to a depth of eight inches. Discing is allowed if the upper eight inches of soil has a texture of sandy loam or coarser. If plowed, furrows must be thrown uphill and there must not be a dead furrow in the original soil mound absorption area. A rubber tired tractor is allowed for plowing or discing. Rototilling or pulverizing the soil is not allowed. The original soil must not be excavated or moved more than one foot from its original location during soil surface preparation.
(18) All surface preparation must take place when the upper 12 inches of soil has a moisture content of less than the plastic limit and soil conditions allow field testing of soil properties and these properties are maintained throughout the installation,
(19) Prior to placement of six inches of clean sand, vehicles must not be driven on the original soil mound absorption area before or after the surface preparation is completed. The clean sand must immediately be placed on the prepared surface.
(20) If rainfall occurs on the prepared surface, the site must be allowed to dry below the plastic limit and roughened as described in § 52.17(C)(17).
(21) The clean sand must be placed by using a construction technique that minimizes compaction. If the clean sand is driven on for construction, a crawler or track-type tractor must be used. At least six inches of sand must be kept beneath equipment to minimize compaction of the prepared surface.
(22) A minimum of 12 inches of clean sand must be placed in contact with the bottom area of the mound distribution media bed and must be uniformly tapered to cover the entire original soil absorption area. Other sandy materials are allowed to be used outside of this area to complete construction of the mound.
(23) The top of the clean sand layer upon which the mound distribution media bed is placed must be level in all directions.
(24) A vertical inspection pipe at least four inches in diameter must be installed and secured at the distribution medium and sand interface. The inspection pipe must have three-eighths inch or larger perforations spaced vertically no more than six inches apart. At least two perforations must be located in the distribution medium. Perforations must not be located above the permeable synthetic fabric, if used. The inspection pipe must extend to the bottom of the distribution medium, be secured, and be capped, flush with or above finished grade.
(25) On slopes of one percent or greater, the upslope edge of the mound absorption bed must be placed on the contour.
(26) The sidewalls of the mound absorption bed must be as vertical as practical and not intentionally sloped.
(27) A minimum of six inches of sand, sandy loam or loam material must be placed on the top of the mound absorption bed and sloped upwards towards the center of the mound a minimum often horizontal units to one vertical unit.
(28) Construction vehicles must not be allowed on the distribution media until backfill is placed as described in division (27) above.
(29) A minimum of six inches of topsoil borrow must be placed over the entire mound.
(30) A vegetative cover must be established over the entire area of the mound. The mound shall be protected until a vegetative cover is established by use of erosion control. The established vegetative cover shall not interfere with the hydraulic performance of the system and shall provide adequate frost and erosion protection.
(D) At-grade systems.
(1) To qualify as an at-grade system, the system must meet or exceed the following requirements:
(a) Employ flow values in § 52.12.
(c) Meet or exceed the requirements of § 52.16(B) and (C).
(d) Meet the requirements of divisions (D)(2) to (14) of this section.
(2) The upper 12 inches of the absorption area must have a loading rate of 0.45 gallons per day per square foot or greater as shown in Table IX in Minn. Rule 7080.21501 or Table VI.
(3) At-grade systems must not be installed in areas with slopes greater than 12%.
(4) Setbacks must be according to Table V. Setbacks must be measured from the original soil absorption area.
Design and construction of at-grade systems.
(5) The at-grade absorption width must be as long and narrow as practical. The at-grade absorption width must not exceed a width of 15 feet. The at-grade absorption widths must be determined by the contour loading rate, which is the relationship between the vertical and horizontal water movement water movement based on the following soil conditions:
(a) The permeability difference between the original soil mound absorption area and slower permeability horizons below the original soil mound absorption area.
(b) The depth between the original soil mound absorption area and the change in permeability described in division (D)(5)(a) of this section.
(c) The land slope.
(6) The minimum at-grade absorption bed width shall be calculated by dividing the contour loading rate by the soil loading rate of the upper 12 inches of soil.
(7) The minimum at-grade absorption length must be calculated by dividing the design flow by the soil loading rate found in Table IX in Minn. Rules 7080.21501 or Table VI for the upper 12 inches of soil and then dividing that value by the absorption bed width.
(8) The at-grade bed absorption width for slopes of one percent or greater does not include any width of the media necessary to support the upslope side of the pipe.
Table VII At-Grade Contour Loading Rates
Perc Rate (mpi) | Loading Rate | Soil Texture | Other Characteristics in upper 48 inches | Contour Loading Rate (GPD/ft) |
<0.l* | 0.00 | Coarse sand | No textural change | 6 |
Saturated soil < 3' Bedrock < 4' | 5 | |||
0.1 to 5.0 | 1.60 | Sand loamy sand fine sand | No textural change | 8 |
Layers of other textures | 7 | |||
Banding | 4 | |||
Saturated soil < 3' | 5 | |||
Bedrock < 4' | 5 | |||
6 to 15 | 1.00 | Sandy loam | Strong to moderate structure No textural change | 7 |
Weak structure Layers of other textures | 6 | |||
Platy or massive structure Saturated soil < 3' Bedrock < 4' | 5 | |||
16 to 60 | 0.6-0.78 | Loam Silt loam Silt Clay loam Sandy clay Silty clay | Strong to moderate structure No textural change | 6 |
Weak structure Layers of other textures | 5 | |||
Platy or massive structure Saturated soil < 3' Bedrock < 4' | 4 | |||
61 to 120 >120 | 0.0-0.3 | Clay Sandy clay Silty clay | Strong to moderate structure No textural change | 3 |
Weak structure Layers of other textures | 2 | |||
Platy or massive structure Saturated soil < 3' Bedrock < 4' | 2 | |||
*See § 52.18(B) for a system with this type of soil (Type II, Rapidly Permeable Soils Systems)
(9) At-grade systems must employ pressurized distribution by meeting or exceeding the applicable requirements of §§ 52.14 and 52.15. At-grade systems located on slopes of one percent or greater require only one distribution pipe located on the upslope edge of the distribution media, with the absorption bed width being measured from the distribution pipe to the downslope edge of the media. Multiple distribution pipes are allowed to be used to provide even distribution, if necessary, based on site conditions.
MISSING PAGES 70, 71
(3) An SSTS must not be located in a floodway and, whenever possible, placement within any part of the floodplain should be avoided. If no alternative exists, a system is allowed to be placed within the flood fringe if the requirements of divisions (C)(4) to (11) are met.
(4) There must be no inspection pipe or other installed opening from the distribution media to the soil surface.
(5) An SSTS must be located on the highest feasible area of the lot and must have the location preference over all other improvements, except the water supply well. If the ten-year flood data are available, the bottom of the distribution media must be at least as high as the elevation of the ten-year flood.
(6) If a pump is used to distribute effluent to the soil treatment and dispersal system, provisions shall be made to prevent the pump from operating when inundated with floodwaters.
(7) When it is necessary to raise the elevation of the soil treatment system to meet the vertical separation distance requirements, a mound system as specified in § 52.17(C) is allowed to be used with the following additional requirements:
(a) The elevation of the bottom of the mound bed absorption area must be at least on-half foot above the ten-year flood elevation, if ten-year flood data are available.
(b) In no case shall the sand fill for the mound exceed 48 inches below the mound bed absorption area.
(c) Inspection pipes must not be installed unless the top of the mound is above the 100-year flood elevation.
(d) The placement of clean sand and other fill must be done according to any community adopted floodplain management ordinance.
(8) When the top of a sewage tank is inundated, the dwelling must cease discharging sewage into it.
(9) Backflow prevention of liquid into the building when the system is inundated must be provided. If a holding tank is used, the system must be designed to permit rapid diversion of sewage into the holding tank when the system is inundated.
(10) If a holding tank is used to serve a dwelling, the holding tank’s capacity must equal 100 gallons times the number of bedrooms times the number of days between the ten-year stage on the rising limb of the 100-year flood hydrograph and the ten-year stage on the falling limb of the hydrograph, of 1,000 gallons, whichever is greater. The holding tank must be accessible for removal of tank contents under flooded conditions.
(11) Whenever the water level has risen above the top of a sewage tank, the tank must be pumped to remove all solids and liquids after the flood has receded and before use of the system is resumed.
(D) Privies.
(1) Privies shall only be considered when there is no water supplied to the dwelling.
(2) Pit privies shall not be installed where the bottom of the pit is less than three feet above the saturated soil or bedrock. A vault privy shall be used in areas not meeting the three foot separation. The vault of a vault privy shall be constructed in the same manner as a sewage tank in accordant with § 52.13.
(3) Privies shall be set back from surface waters, buildings, property lines, and water supply wells prescribed in Table V.
(4) Pits or vaults shall be of sufficient capacity for the dwelling they serve, but shall have at least cubic feet of capacity. The sides of the pit shall be curbed to prevent cave-in. The privy shall 1 constructed so as to be easily maintained and it shall be insect proof. The door and seat shall 1 self-closing. All exterior openings, including vent openings, shall be screened.
(5) Privies shall be adequately vented.
(6) When the privy is filled to within one foot of the top of the pit, the solids shall be removed.
(7) Abandoned pits shall have the solids removed and be filled with clean earth and slightly mounded to allow for settling. Removed solids shall be disposed of in accordance with § 52.22.
(E) Holding tanks.
(1) Holding tanks may be considered for installation on previously developed sites, as a temporary method for periods of up to 12 months, during which time measures are taken to provide municipal sewer service or the installation of an approved system as provided in this chapter.
(2) Holding tanks may be considered on a permanent basis for non-residential, low water use establishments with a sewage flow of 150 gallons per day or less, subject to approval by the Department or local unit of government.
(3) Holding tanks must be used for floor drains for vehicle parking areas and existing facilities potentially generating hazardous waste.
(4) To qualify as a holding tank, the system must:
(a) Meet or exceed applicable requirements of § 52.13.
(b) Meet or exceed the applicable requirements of § 52.16(B).
(c) Meet or exceed the requirements of § 52.16(C)(2).
(d) Meet the requirements of § 52.18(E)(2) to (10).
(5) All tanks used as holding tanks must be tested once placed at the final location for watertightness as specified in Minn. Rule § 7080.2010.
(6) A cleanout pipe of at least six inches in diameter must extend to the ground surface and be provided with seals to prevent odor emissions and exclude insects and vermin. A maintenance hole of at least 20 inches in least dimension must extend through the cover to a point within 12 inches, but not closer than six inches, below finished grade. If the maintenance hole is covered with less than six inches of soil, the cover must be secured according the § 52.13(M).
(7) For a dwelling, the minimum size is 1,000 gallons or 400 gallons times the number of bedrooms, whichever is greater. For other establishments, the minimum capacity shall be at least five times the design flow. Tank sizing for floodplain areas must be calculated according to division (C)(10) of this section.
(8) Holding tanks must be located in an area readily accessible to the pump truck under all weather conditions and where accidental spillage during pumping will not create a nuisance and must meet the setback requirements of Table V.
(9) Holding tanks must have an alarm device to minimize the chance of accidental sewage overflow unless regularly scheduled pumping is used. An alarm device shall identify when the holding tank is at 75% capacity.
(10) A contract for disposal and treatment of the septage shall be maintained by the owner with a licensed maintainer.
(Ord. 2010-162, passed 5-17-2010)