§ 52.16 TREATMENT AND DISPERSAL.

   (A)   Treatment and dispersal of all sewage for new construction or replacement SSTS must in compliance with this Section and §§ 52.17 to 52.21.

   (B)   All new construction or replacement SSTS must he designed to meet or exceed the following provisions:

      (1)   All treatment and dispersal methods must be designed to conform to all applicable federal, state, and local regulations.

      (2)   Treatment and dispersal processes must prevent sewage or sewage effluent contact with humans, insects, or vermin.

      (3)   Treatment and dispersal of sewage or sewage effluent must be in a safe manner that adequately protects from physical injury or harm.

      (4)   An unsaturated zone in the soil must be maintained between the bottom of the soil treatment and dispersal system and the periodically saturated soil or bedrock during loading of effluent.

      (5)   Soil treatment and dispersal systems must not be designed in floodways. Soil treatment and dispersal systems installed in flood fringes must meet the requirements of § 52.18(C). All soil treatment systems located in areas subject to excessive run-on must have a diversion constructed upslope from the system.

      (6)   SSTS components must be setback in accordance with Table V.

      (7)   No component of an SSTS is allowed to be located under or within the structure or other impermeable surface.

      (8)   Flow measurement must be employed for all single family dwellings and other establishments with a pump tank, all single family dwellings with a Type III, IV, V systems, and all multi-family dwellings.

Table V - Minimum Setback Distances (Feet)

Feature	Sewage Tank	Soil Treatment and Dispersal Area
Water supply wells less than 50 feet deep and not encountering at least 10 feet of impervious material	50	100
Any other water supply well or buried suction pipe	50	50
Buried pipe distributing water under pressure	10	10
Occupied buildings and buildings with basements or crawl spaces	10	20
Non-occupied structures	5	10
Property lines	10	10
Above ground and in-ground swimming pools	10	10
The Ordinary High Water Mark of:
Natural environment lakes and streams	150	150
Recreational development lakes and streams	75	75
General development lakes and streams	75	75
All unclassified waters	75	75
St. Croix River-rural districts	150	150
St. Croix River-urban districts	100	100
Blufflines:
St. Croix River blufflines	40	40
Shoreland blufflines	20	20

 

   (C)   The following items are required for specific designs as determined in §§ 52.17 to 52.21.

      (1)   Employ components registered under Minn. Rules 7083.4070 and 7083.4080 that are installed, used and operated according to the conditions placed on the registration.

      (2)   Employee structural components and joint sealants that meet or exceed the system’s expected design life.

      (3)   For acceptable treatment of septic tank effluent by soil, the soil treatment and dispersal systems must meet the following requirements:

         (a)   A minimum three-foot vertical soil treatment and dispersal zone shall be designed below the distribution media that meets the following criteria:

            1.   The zone must be above the periodically saturated soil and bedrock. The zone must be continuous and not be interrupted by seasonal zones of saturation.

            2.   Any soil layers with a texture group of 1 in Table IX in Minn. Rules 7080.2150 must not be credited as part of the necessary three-foot zone.

            3.   The entire treatment zone depth must be within seven feet from final grade.

         (b)   The distribution system or media must not place a hydraulic head greater than 30 inches above the bottom of the absorption area.

      (4)   The system’s absorption area must be in original soil.

      (5)   The system’s absorption area must be sized according to the Table IX-Loading Rate for Determining Bottom Absorption Area for Trenches and Seepage Beds for Effluent Treatment Level C and Absorption Ratios for Determining Mound Absorption Areas Using Detailed Soil Descriptions as found in Minn. Rules Chapter 7080.21501, or by using Table VI if not using detailed soil descriptions. Soils with a loading rate less than 0.45 gallons per day per square foot cannot be used in a Type I or Type II system for new construction.

Table VI
Loading Rates for Determining Bottom Absorption Area for Trenches and Seepage Beds for Effluent Treatment
Level C and Absorption Ratios for Determining Mound Absorption Areas Using Percolation Test

Percolation Rate (Minutes per Inch)	Soil Loading Rate (gpd/ft2)	Mound Absorption Ratio
<0.1*	-	-
0.1-5*	1.20	1
0.1-5 (Soil Texture Group 3)	0.6	2
6-15	0.78	1.3
16-30	0.6	2
31-45	0.5	2.4
46-60	0.45	2.6
>60**	0.24	5.0

 

* See § 52.18(B) for a system with this type of soil (Type II, Rapidly Permeable Soils Systems)

** Soil with too high a percentage of clay for installation of a Type I, or Type II system. Systems in soils with this Percolation Rate must be a Type III, Type IV or Type V system.

      (6)   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.

      (7)   All excavation into the absorption area, or surface preparation of the upper 12 inches of the 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,

      (8)   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 the media or designed coverage materials. If the areas are exposed to direct rainfall, they must be allowed to dry and must be re-prepared according to § 52.16(C)(7).

      (9)   A minimum of six inches of topsoil borrow shall be placed over the system.

      (10)   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 vegetation establishment shall begin immediately after the placement of the topsoil borrow. The soil treatment and dispersal system must be protected from erosion and excessive frost until a vegetative cover is established. The vegetative cover established must not interfere with the hydraulic performance of the system and shall provide adequate frost and erosion protection. Trees, shrubs, deep-rooted plants, or hydrophytic plants must not be planted on the system.

   (D)   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 Minn. Rules 4725.0100, subpart 21, must employ best, management practices for nitrogen reduction developed by the Commissioner to mitigate water quality impacts to groundwater.

   (E)   Final treatment and dispersal for MSTS shall meet the following requirements:

      (1)   Final treatment and dispersal must be according to applicable design requirements of this chapter, except as modified in this section. Code of Federal Regulations, Title 40, Parts 144 and 146, prescribe additional design regulations applicable to certain systems. At a minimum, flow amounts to be used for the purpose of this section must be derived from Table II in § 52.12.

      (2)   MSTS must meet all setbacks in Table V.

      (3)   The site proposed to support the soil treatment and dispersal system must:

         (a)   Have the upper 18 inches of the absorption area:

            1.   Be original soil.

            2.   Have a soil loading rate of greater than zero as listed in Table IX in Minn. Rules 7080.21501 or Table VI in § 52.16(C).

            3.   Be above the periodically saturated soil or bedrock.

         (b)   Meet the area size requirements in division (E)(5) of this section and setbacks in Table V.

         (c)   Not be a wetland or floodway.

         (d)   Not be in an area in which surface runoff from precipitation will concentrate (concave hillslope).

         (e)   Allow the system to be placed on contour.

      (4)   Inspection pipes must be located to adequately assess the hydraulic performance of the entire soil dispersal system.

      (5)   Effluent loading rates to the soil shall be no greater than loading rates prescribed in:

         (a)   Table IX in Minn. Rules 7080.21501, or Table VI in division (C) of this section, if the absorption area receives treatment level C effluent as defined in Minn. Rules 7083.4030.

         (b)   Table XII in Minn. Rules 7080.23504, or Table X in § 52.20(E), if the absorption area receives treatment level A or B effluent in part Minn. Rules 7083.4030.

         (c)   Section 52.21.

      (6)   If the absorption area receives effluent as described in § 52.16(E)(5)(a), the absorption area shall be increased by 50% of the amount derived in § 52.16(E)(5)(a), and zoned for dosing and resting.

      (7)   The system geometry and lawn area sizing shall be sized to prevent groundwater mounding from violating the unsaturated zone beneath the soil system according to § 52.16(E)(8) for proper hydraulic functioning, and for concentration reduction of nitrogen and phosphorus, if applicable.

      (8)   Additional set-aside land area of 100% of the size determined in § 52.16(E)(7) is required for systems whose absorption area receives effluent meeting treatment level A or B in part Minn. Rules 7083.4030 or designed in accordance with § 52.21. Additional land area of 5% of the size determined in § 52.16(E)(1) is required for systems whose absorption area receives treatment level C in part Minn. Rules 7083.4030. The reserve land area must be identified and protected for future use if necessary. Replacement MSTS proposed on sites that cannot meet this requirement are allowed to be exempted by the Department or local unit of government.

      (9)   For treatment of effluent by soil to meet the performance criteria in § 52.09(C) of this chapter the soil treatment and dispersal systems must meet the requirements below:

         (a)   For soil treatment and dispersal systems that receive treatment level C effluent as describe in Minn. Rules 7083.4030, the soil treatment zone requirements must meet or exceed the requirements of § 52.16(C)(3). The required three-foot vertical separation must be maintained during operation after accounting for groundwater mounding.

         (b)   For soil treatment and dispersal systems that receive treatment level A or B effluent as described in Minn. Rules 7083.4030, the soil treatment requirements must meet or exceed the following requirements:

            1.   A minimum vertical depth of the soil treatment and dispersal zone below the distribution media shall be determined according to Table IX in § 52.20. with a minimum vertical separation of two feet. This zone shall meet the following criteria:

               a.   The zone must be above the periodically saturated soil and bedrock. The zone must be continuous and not be interrupted by seasonal zones of saturation.

               b.   Any soil layers with a texture group of 1 in Table IX in Minn. Rules Chapter 7080.21501 must not be credited as part of the necessary treatment zone.

               c.   The entire treatment zone depth must be within seven feet from final grad

            2.   The distribution system or media must not place a hydraulic head greater than 30 inches above the bottom of the absorption area.

            3.   The system’s absorption area must be original soil.

            4.   The systems absorption area must be sized according to § 52.16(E)(5).

         (c)   The minimum vertical separation can be determined by the method described in § 52.21 to meet provisions of § 52.04(I)(3).

         (d)   An observation well to measure the height of the periodically saturated soil beneath the operating system must be installed and monitored according to the operating permit.

      (10)   MSTS systems must employ nitrogen mitigation methods to achieve compliance with § 52.09(D), and must be monitored in accordance with § 52.11(D).

      (11)   Phosphorus mitigation methods must be employed to achieve compliance with § 52.09(E), if natural processes are found inadequate.

      (12)   All information required in this Section shall be submitted for review and approval by the Department or local unit of government prior to system construction, including all applicable information delineated on a map.

   (F)   MSTS construction must be according to applicable construction requirements of this chapter.

   (G)   The design standards for new construction or replacement MSTS are provided to meet many of the public health and environmental outcomes in § 52.04. In some cases, specific design methods must be employed in addition to the standards provided in this chapter.

   (H)   MSTS must not receive storm water or other sources of clean water.

   (I)   All structural components of the system and sealants must be designed to operate throughout the system’s design life.

   (J)   A flow measure device must be employed on all MSTS.

   (K)   The system must be designed with sufficient access and ports to monitor the system as applicable.

   (L)   MSTS must employ components registered under parts 7083.4000 to 7083.4110 or have sufficient regulatory oversight in the operating permit.

   (M)   The MSTS designer must observe critical periods of the system construction. The designer shall prepare a report of observed construction activities and submit the report to the Department or local unit of government prior to the final inspection.

(Ord 2010-162, passed 5-17-2010)