(A) Purpose; requirements. The intent of this section is to provide standards for the location, design, installation, use and maintenance of alternative sewage treatment systems. Alternative systems must meet the requirements below and can only be used when a standard system cannot to be installed or is not the most suitable treatment. They may be employed provided:
(1) Reasonable assurance of performance of the system is presented to the permitting authority;
(2) The engineering design of the system is first approved by the permitting authority;
(3) There is no discharge to the ground surface or to the surface water; systems designed with a ground surface or surface water discharge are not covered under this chapter and must obtain a National Pollution Discharge Elimination System (NPDES) permit or state disposal system (SDS) permit from the Minnesota Pollution Control Agency;
(4) A 3-foot minimum separation is provided between the bottom of the distribution medium and the saturated soil or bedrock;
(5) Treatment and disposal of wastes is completed in a manner that protects the public health and general welfare;
(6) The system complies with all local codes and ordinances and is subject to periodic inspections by the permitting authority to assure adherence to specifications;
(7) A mitigative plan is provided to the permitting authority indicating what will be done if the system fails to provide treatment and disposal; and
(8) A water meter is provided (located down flow of any outside sillcocks) to verify water use.
(Prior Code, Ch. 506 § 15.1)
(B) Artificial drainage.
(1) Where natural drainage does not provide 3 feet of separation, artificial drainage may be used to intercept the high water table provided the water table has a slope of at least 2 feet per 100 feet and that drainage exists upslope of the soil treatment system. There shall be at least 10 feet of undisturbed soil between the sidewall of the soil treatment unit and the artificial drainage. Monitoring may be required.
(2) Where required, water table measuring piezometer shall be strategically placed, capped, and extended at least 3 feet lower than the bottom of the soil distribution medium. Monitoring shall occur by measuring water table depths prior to installation and over time, including during wet periods. Monitoring records must be maintained. If the artificial drain includes a dedicated surface discharge, periodic sampling as approved by the permitting authority must occur.
(3) In all cases, the greatest practicable vertical separation distance from the system bottom to saturated soil shall be provided (with a minimum of 3 feet).
(Prior Code, Ch. 506 § 15.2)
(C) Floodplain areas.
(1) There shall be no pipe or other installed opening between the distribution medium and the soil surface.
(2) Trench systems shall be located on the highest feasible area of the lot and shall have location preference over all other improvements except the water supply well. The bottom of the distribution medium shall be at least as high as the elevation of the 10-year flood. The sewage tank may be located so as to provide gravity flow to the trenches.
(3) If a dosing chamber is used to move effluent from the sewage tank to the trenches, provisions shall be made to prevent the pump from operating when inundated with floodwaters.
(4) When it is necessary to raise the elevation of the soil treatment area, a mound system as specified in § 157.38(J) may be used with the following additional requirement: In no case shall the sand fill for the mound exceed 48 inches below the rock bed. The elevation of the mound shall be such that the elevation of the bottom of the rock bed shall be at least 1/2 foot above the 10-year flood elevation. Inspection pipes shall not be installed unless the top of the mound is above the elevation of the regional flood.
(5) When the top of a sewage tank is inundated, the dwelling must cease discharging sewage into it. This may be accomplished by either temporarily evacuating the structure until the system again becomes functional, or by diverting the sewage into a holding tank sized and installed according to division (H) of this section.
(6) The building sewer shall be designed to prevent backflow of liquid into the building when the system is inundated. If a holding tank is used, the building sewer shall be designed to permit rapid diversion of sewage into the holding tank when the system is inundated.
(7) Whenever the water level has reached a stage above the top of a sewage tank, the tank shall be pumped to remove all solids and liquids after the flood has receded before use of the system is inundated.
(Prior Code, Ch. 506 § 15.3)
(D) Grey water systems. A toilet waste treatment device shall be used in conjunction with a grey water system. In all cases, only toilet wastes shall be discharged to toilet waste treatment devices. Grey water or garbage shall not be discharged to the device as specifically recommended by a manufacturer.
(1) Plumbing. The drainage system in new dwellings or other establishments shall be based on a pipe diameter of 2 inches to prevent installation of a water flush toilet. There shall be no openings or connections to the drainage system, including floor drains, larger than 2 inches in diameter. For repair or replacement of an existing system, the existing drainage system may be used. Toilets or urinals of any kind shall not be connected to drainage systems. Toilet waste or garbage shall not be discharged to the drainage system. Garbage grinders shall not be connected to the drainage system.
(2) Building sewer. The building sewer shall meet all requirements of § 157.15(C) except that the building sewer for grey water system shall be no greater than 2 inches in diameter.
(6) Final treatment and disposal. A standard grey water system shall meet all requirements of § 157.38.
(Prior Code, Ch. 506 § 15.4)
(E) 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 3 feet above the saturated soil or bedrock. A vault privy shall be used in areas not meeting the 3-foot separation. The vault of a vault privy shall be constructed in the same manner as a sewage tank.
(3) Privies shall be set back from surface waters, buildings, property lines, and water supply wells as prescribed in Table III.
(4) Pits or vaults shall be of sufficient capacity for the dwelling they serve, but shall have at least 50 cubic feet of capacity. The sides of the pit shall be curbed to prevent cave-in. The privy shall be constructed so as to be easily maintained and it shall be insect-proof. The door and seat shall be 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 1 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 § 157.41(H).
(Prior Code, Ch. 506 § 15.5)
(F) Other toilet waste treatment devices.
(1) Other waste toilet treatment devices may be used where reasonable assurance of performance is provided.
(2) All devices shall be vented.
(3) All electrical, gas, and water connections shall conform to all local ordinances and codes.
(4) Operation and maintenance shall follow the manufacturer's recommendation.
(Prior Code, Ch. 506 § 15.6)
(G) Collector systems.
(1) Where site and soil conditions do not allow for final treatment and disposal on an individual lot, a soil treatment system located on another lot or lots may be employed.
(2) Except for systems designed for 1,200 gallons per day or less, collector systems shall be designed by a registered professional engineer, licensed in the state, and certified by the MPCSA as competent in the field of on-site system design.
(3) Hydrogeologic study: Due to the effect large flows have on groundwater quality and groundwater mounding, a hydrologist shall determine site suitability based on the following. A hydrogeologic study may not be required for a collector system designed for 1,200 gallons per day or less.
(a) Identification of the depth of the static groundwater level and any perched water or areas likely to be seasonally saturated;
(b) Identification of the depth to bedrock;
(c) Identification of the proposed depth of the distribution medium;
(d) Determination of the direction of groundwater flow, both horizontally and vertically;
(e) Determination of the background water quality at the location;
(f) Estimation of the height of groundwater mounding from the proposed system to confirm adequate vertical separation;
(g) Determination whether drinking water standards can be met at the property boundary; and
(h) Estimation of the impact of water quality on existing or future downstream wells. Depending on this estimate, piezometer and/or monitoring wells may be required.
(4) Application to the Department shall be accompanied by the hydrogeologic study and engineering drawing and specifications and shall demonstrate compliance with all applicable local ordinances, the Plumbing Code and issues related to joint ownership of land, joint systems maintenance responsibilities, homeowners' associations, easements, covenants, and such other items as may apply to the specific proposal.
(5) Design.
(a) Sewer systems shall be designed based on the sum of the areas required for each dwelling or other establishment being served. Flows shall be increased to allow for 200 gallons of infiltration per inch of pipe diameter per mile per day.
(b) The system shall be designed with each dwelling or other establishment having a sewage tank or with a common sewage tank. In the case of a common tank, the capacity of the tank shall be the sum of the tanks sized according to § 157.35(G).
(c) The sum of a common soil treatment system shall be based on the sum of the areas required for each dwelling unit or establishment being served.
(d) The sewer for systems with common sewage tanks shall be constructed to give mean velocities, when flowing full, of not less than 2 feet per second. The sewer for systems with individual sewage tanks shall be so constructed and designed to hydraulically conduct the flow for which they were designed. In no case shall a gravity sewer be less than 4 inches in diameter. The diameter and grade line should be based on a flow equal to 50% of the average design flow occurring in a 1-hour period.
(e) Infiltration or exfiltration shall not exceed 200 gallons per inch of pipe diameter per mile per day.
(f) Cleanouts, brought flush with or above finished grade, shall be provided wherever a common sewer joins an individual building sewer or piping from an individual sewer tank, or every 100 feet, whichever is less, unless maintenance hole access is provided.
(g) There shall be no physical connection between sewer and water supply systems. Sewers shall be set back from water supply systems and piping as required for building sewers. Where it is not possible to obtain proper separation, the sewer connections shall be watertight and pressure tested.
(h) Pipes and pipe joints shall be watertight.
(i) Dosing chambers shall meet all requirements in § 157.37(A).
(j) Pumps and dosing chambers shall be sized to handle 50% of the average design flow in a 1-hour period. Common pump tanks shall have a pump out capacity of 10% of average design flow and 2 alternating pumps.
(k) A separate alarm system for each pump shall be provided for all pumping stations to warn of pump failure, overflow, or other malfunction.
(l) For systems with individual septic tanks, a stilling tank of a least 1,500 gallons liquid capacity or 10% of the average design flow, whichever is greater, should be provided before the soil treatment system.
(m) Pump stations shall have maintenance holes flush with or above finished grade for cleaning and maintenance. Maintenance covers shall be secured so as to prevent unauthorized entry.
(n) All persons using a common individual sewage system shall assure, by contract with maintenance personnel or other equivalent means, that the system will be maintained throughout its useful life. The system so maintained includes common soil treatment systems, common sewage tanks, common pumps, common pump stations, common sewers, and all individual tanks connected to the common system.
(Prior Code, Ch. 506 § 15.7)
(H) Holding tanks.
(1) Sewage holding tanks may be considered for installation on previously developed sites, as a temporary method for periods of up to 1 year, during which time measures are taken to provide municipal sewer service or the installation of an approved system as provided in this chapter. Holding tanks may be considered on a permanent basis for nonresidential, low water use establishments generating less than 150 gallons per day of waste, subject to the approval of the Department. Holding tanks may also be considered for floor drains for vehicle parking area and existing facilities potentially generating a hazardous waste.
(2) A holding tank shall be constructed of the same materials and by the same procedures as specified in this chapter for sewage tanks, § 157.35.
(3) A cleanout pipe of at least 6 inches diameter shall extend to the ground surface and be provided with seals to prevent odor and to exclude insects and vermin. A maintenance hole of at least 20 inches in dimension shall extend through the cover to point no less than 6 inches below the finished grade. If the maintenance hole is covered with less than 6 inches of soil, the cover must be secured to prevent unauthorized access.
(4) When installed in areas of high groundwater within 6 feet of the ground surface, holding tanks shall be installed entirely above the groundwater level or shall be installed according to an engineer's design to prevent flotation.
(5) For a dwelling, the minimum size shall be 1,200 gallons or 400 times the number of bedrooms, whichever is greater. For other establishments, the minimum capacity shall be based on measured or estimated flow rates. Minimum capacity shall be equal to at least 8 times the average design flow.
(6) Holding tanks shall be located as specified for sewage tanks in Table III; in an area readily accessible to the pump truck under all weather conditions; and where accidental spillage during pumping will not create a nuisance.
(7) A contract for disposal and treatment of the septage shall be maintained by the owner with a pumper, the city or firm established for that purpose.
(8) Holding tanks shall be monitored to minimize the chance of accidental sewage overflows by installation of an alarm or warning device which will activate a signal when the tank reaches 75% of its capacity.
(9) The permitting authority shall be provided right of access to perform periodic maintenance and operational inspections of the system.
(Prior Code, Ch. 506 § 15.8)