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HomeMy WebLinkAboutResolution 983RESOLUTION NO. 983 A RESOLUTION AMENDING CERTAIN SECTIONS OF RESOLUTION NO. 894, THE CITY OF ORONO ON- SITE SEWAGE TREATMENT SYSTEM DESIGN MANUAL WHEREAS, the City of Orono is a municipal corporation organized and existing under the laws of the State of Minnesota; and WHEREAS, the City Council of the City of Orono adopted Resolution No. 894 on the Thirteenth day of April, 1978, to provide standard practices and required specifications for the construction, repair or alteration of any on-site sewage treatment system within the City of Orono; and WHEREAS, certain construction standards and practices should be revised to clarify procedures and ensure uniformity in the quality and reliability of septic sys,.tem design, construction and installation, NOW, THEREFORE, BE IT RESOLVED, that the City Council of the City of Orono hereby makes the following changes in Resolution No. 894, The City of Orono On -Site Sewage Treatment System Design Manual: I.' Revise Part III, Section 3, Soil Borings, to read: Soil Borings at least 8 feet deep (S feet below the bottom of any proposed drainfield trench) shall be taken to determine soil types and water table information. For new systems, at least two (2) borings shall be made within the primary drainfield area and at least one (1) boring within the alternate drainfield area. For drainfield additions to existing systems, at least one (1) soil boring is required. Soil borings shall identify depth at which soil is mottled, indicating the depth -of seasonal water table. 2. Revise Part III, Section 4, Percolation Testing, to read: Percolation testing shall be done on all proposed drainfield sites to help determine the natural absorption capability of the soil. For new systems, at least four (4) percolation tests shall be made within the primary drainfield area and at least two (2) percolation tests within the alternate drainfield area. For drainfield additions to existing systems, at least two (2) percolation tests should be made in the expansion area. E Resolution No. 983 Page 2 2. Cont. Percolation Test Procedure 1. Type of Test Hole A hole with horizontal dimensions of 6" and vertical sides shall be dug or bored to the depth of the proposed absorption trench. 2. Preparation of Test Hole The bottom and sides of the hole shall be carefully scratched With a knife blade or sharp pointed instrument to remove any smeared soil surfaces and to provide a natural soil interface into which water may percolate. All loose material shall be removed from the hole and two (2) inches of coarse sand or fine gravel shall be added to protect the bottom from scouring and sediment. , .3. Saturation and Swelling of the Soil . The hole shall be carefully filled with clear water to a minimum depth of 12" over, the gravel. Water shall be kept in the hole for at least four (4) hours., and preferably overnight by refilling if necessary, or by supplying a surplus reservoir of water, such as in an automatic siphon. In sandy soils containing little or no clay, the swelling procedure shall not be required and the test may be made after the water from one filling of the hole _ has completely seeped away. 4. Percolation Rate Measurement With the exception of sandy soils, percolation rate measurements shall be made on the day following the procedure described under Items 1 - 3 above. A. If water remains in the hole after the overnight swelling period, bail out all but 6" of the water above the fine gravel (8" if measured from the bottom of the hole). Then measure the drop in water level 'to the nearest 1/16" approximately every 30 minutes. Use a measuring stick with the top of a level batter board as a reference point.. Continue the test until the extremes of three consecutive measurements vary by a range of no more than 10%. Resolution No. 983 • Page 3 2. Cont. B. If no water remains in the hole after the overnight swelling period, add 6" of clear water above the fine gravel. Every 30 minutes, measure the drop in water level to the nearest 1/16". Continue the percolation rate measurements until the extremes of three consecutive measurements vary by no more than 10%. Refill the .hole as often as necessary to bring the water to 8" above the bottom. C. In sandy soils (or other soils in which the first 6" of water seep away in less than 30 minutes after the overnight swelling period), allow 10 minutes between measurements. Continue the tests until the extremes of three consecutive measurements vary by no more than 10%. A log shall be kept and submitted of all percolation tests showing diameter and depth of hole, soil profile percolation rate expressed in minutes per inch and ground water conditions if encountered. 3. Revise Part IV, Section 2 Standard System Design, Item 1(c) isto read: Septic tanks shall be placed so that access is convenient for the removal of liquids and accumulated solids. The tanks shall be placed on,firm and settled soil capable of bearing the weight of the•tank and its contents. Minimum setback distances for tanks shall be the same as for treatment areas, with this exception: minimum tank setback from buildings - 10 feet. 4. Add Item 1(d) Site -constructed concrete block tanks shall be allowed only where topography or other site factors preclude the use of precast concrete, sectional, or fiberglass tanks. S. Revise Item 3(a)to read: All treatment areas shall be setback the following horizontal distance from the features given below: Feature Minimum Setback Distance (Feet) -Property Lines and Buried Pipes Distributing Water Under Pressure 20 -Water Supply Wells or Buried Water • Suction Pipes 75 -Lakes, Streams and Wetlands 75 -Buildings, paved areas & other hardcover 20 -Vertical Separation between Bottom of Filter Rock and Seasonal High Water Table or Bedrock 3 Resolution No. 983 Page 4 • 6. Revise Part V, Section 2, Building Sewers, Item 3, to read: The buried or concealed portion of any building sewer, building drain or branch thereof shall be located at least 20 feet from any well. The Building sewer shall be constructed of city approved pipe material with air tested joints. The Air test should be made by attaching an air compressor or test apparatus to a suitable opening.and closing all other inlets or outlets to the sewer and/or. drain under test by means of proper testing plugs. Air shall be forced into the system until there is uniform pressure of five pounds per square inch in the section being tested. The system shall be considered satisfactorily air tested if the pressure therein remains constant for 15 minutes without the addition of air. 7. Revise Part V, Section 6, Item B, Design and Construction, (1) to read: The bottom of the filter material in trenches and beds shall be at least three (3) feet above the seasonal high water table or bedrock. • 8. Revise Part V, Section 8, Item E, Distribution of Sewage, to read: It is strongly recommended that a pressure distribution system be utilized to provide equal distribution of the sewage effluent over the entire soil absorption area. 9. Add Part V, Section 10, Innovative Fill Trench System A. Applicability-- This system is intended for areas of moderately slow permeability where depth to groundwater is acceptable for a standard trench system. 1. Percolation Rate - The percolation rate of the original soil shall be more than 60 and not more than 90 minutes per inch. 2. Depth to Groundwater - Depth to groundwater or seasonally saturated area must be greater than 5 feet. 3. Flood Hazard - There shall be no hazard of flooding within the area considered for installation of the system. 4. Slope - The land slope in the area being considered for installation of the system must not be greater than 12%. Resolution No. 983 Page 5 • 9. Cont. A. 5. Soils - The following soil classification series will in many cases be considered unsuitable for the installation of standard systems, but acceptable for a properly designed fill trench system. Erin - EnB, EnC Hayden - HbB, HbC, HcB2, HcC2 Heyder - HeB, HeC Lester - LrB, LrC, LsB2, LsC2 B. General Requirements 1. In no case shall excavation for the purpose of constructing a fill trench system be made unless the moisture content is lower than the plastic limit of the soil. 2. In no case shall filter material be placed in contact with original soil having a percolation rate slower than 60 minutes per inch. 3. At least 6" but no more than 12" of fill material • having a percolation rate of between 5 and 30 minutes per inch (loamy sands and loams) after placement shall be placed between the filter material and the original soil along the excavation bottom and sidewalls. 4. The size of the soil treatment system shall be based on the required treatment area for a soil having a percolation rate of 60 minutes per inch. 5. All other requirements of standard drainfield trenches as of Section 6 apply. 6. A pressure distribution system is strongly recommended for use with fill trenches. Passed by the City Council of the City of Orono on the —twenty—third day of January 19 79 f William B. Van Nest, Mayor ATTEST: • iC Waiter R. B son, Clerk/Administrator