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HomeMy WebLinkAbout1978-09-14 Septic System Design Reportr • *WOO* 545 Indian Mound Wayzata, Minnesota 55391 September 14, 1978 (612) 473-4224 Mr. David Nitz David Nitz, Inc. 491 West Ferndale Road Wayzata, Minnesota 55391 Re: Percolation Test and Systems Design for a Building Permit, Lot 9, Block 1, Fairview Addition, Orono, Minnesota Job Number 11-78-49 Dear Mr. Nitz: Enclosed is information requested in regards to the septic field suit- e ability of Lot 9, Block 1, Fairview Addition. The drainfield information is based on percolation tests and soil bor- ings performed on September 7 and 8, 1978. The soil found on the site is Lester loam. The soil is mapped in Figure 1. The percolation rate for the primary field as tested was • 27.5 Min./inch. The percolation rate for the secondary field as tested was 23.3 Min./inch. The locations of the percolation test holes, soil borings, and the proposed drainfield areas are indicated in Figure 1. Percolation rates and depths to the water table are shown in Table 1. The soil logs of the soil borings are shown in Table 2. Because of the acceptable percolation rate and because of the acceptable depth to the water table, a conventional on -site treatment system is recommended for the areas shown in Figure 1. I have enclosed plans and specifications for such a system. Additional copies of the plans and specifications are available upon request. Stated percolation rates are averaged for the locations shown, and no guarantee is implied or exrressed that these conditions exist for the entire test area. If you have any questions, please do not hesitate to contact me. Sincerely, EUGENE A. HICKOK AND ASSOCIATES James P. DeBenedet, P.E. S JPD/jel Enclosures • TAB LE 1 PERCOLATION RATES AND DEPTH TO WATER TABLE Hole Percolation Rate (Minutes Inch) P1 30.0 P2 30.0 P3 15.0 P4 3.9 P5 34.3 P6 20.0 Sbl Sb2 Sb3 Depth to Water Table (Feet) 7.3 7.0 Greater than 8.0 Percolation rate of the primary field (holes 1,2,5,6) 27.5 minutes/inch Percolation rate of the secondary field (holes 2,3,5) 23.3 minutes/inch 0 TABLE 2 SOIL LOGS SOIL BORING 1 Depth (Feet) Material 0.0' - 0.5' Brown sandy loam 0.5' - 4.5' Brown sandy clay 4.5' - 8.0' Yellowish brown silty clay, slight mottling at 7.31. The water level was recorded at a depth of 6.91, 24 hours after the hole was augered. However, rain may have influenced this measurement. SOIL BORING 2 Depth (Feet) Material 0.0' - 0.5' Grayish brown sandy loam 0.5' - 1.2' Grayish brown sandy clay loam 1.2' - 8.0' Yellowish brown silty clay, mottled at 7.0'. The water level was recorded at a depth of 6.51, 24 hours after the hole was augered. However, rain may have influenced this measurement. SOIL BORING 3 Depth (Feet) Material 0.0' - 0.5' Grayish brown loam 0.5' - 1.5' Dark yellowish brawn silty clay 1.5' - 3.0' Brown silty clay 3.0' 3.5' - 3.5' - 5.0' Yellowish brown sandy Yellowish brown silt, clay w/s fine sand and pebbles 5.0' - 6.5' Yellowish brown silty clay, w/s 6.5' - 8.0' calcareous material Light yellowish brown clayey silt, w/s fine sand The water level was not recorded within 8.0' of the surface 24 hours after the hole was augered. P 9 �� I.ESTE�. I,UPt 1 / 2'rdvo ` bs.c" I sg- i Oi NNFI i Sr3Z , >01 l�Il.W Fi EL+.) i• I e < 4ci-A, ax,0,1 !(* I •� rl%oFcf::Ei'� t i d EA. HOW 8 ASSOCIATES tiff 11> HYOROLOGW 3-L k3NEERS MMEAPOLIS-MNNESOTA 4.-orv1053ww-sl"lodv3NNw s3.LvrJMV V )0o + •v3 -r- 4-, 'or447VC, J (� V cr- I<A 17 FA IS 8 IN� rl •! 4.-orv1053ww-sl"lodv3NNw s3.LvrJMV V )0o + •v3 -r- 4-, 'or447VC, J (� V cr- I<A 17 FA IS 8 IN� rl •! SPECIFICATIONS FOR PROPOSED ON -SITE SEWAGE DISPOSAL SYSTEM CONVENTIONAL SYSTEM: DISTRIBUTION THROUGH GRAVITY FLOW LOCATION: Lot 9, Block 1, Fairview Addition, Orono, Minnesota Job Number 11-78-49 DATE: September 14, 1978 I. SEWAGE TANK - TWO 1000-gallon LIQUID CAPACITY tanks, IN SERIES, m;:.nufactured and installed in compliance with the following specifications. See Figure 1 for location. 1. MATERIALS A. General All tanks, regardless of material or method of construction shall be: (1) Water tight • (2) So designed and constructed as to withstand all lateral earth pressures under saturated soil conditions with the tank empty (3) So designed and constructed as to withstand a minimum of seven feet of saturated earth cover above the tank top. In addition, the following specifications apply to specific mater- ials as indicated. B. Precast Concrete Tanks (1) Precast concrete tanks shall be constructed of at least a 4,000 psi (pounds per square inch) core test, air entrained concrete mix. (2) Precast concrete tanks shall be cured to at least a seven-day strength before .installation. C. Fiberglass and Plastic Tanks Fiberglass and plastic: tanks shall be designed and constructed to meet the requirements in Section I. - A. �J / , D. Metal Tanks Metal tanks shall have a wall thickness of at least eight gauge corrosion resistant alloys and shall be coated inside and out with at least one coat of bitumastic seal, Koppers 300-M, or by other equivalent means. Tanks shall be carefully installed so as not to puncture or damage the seal coating. E. Block or Sectional Tanks (1) Rectangular Blocks (a) Rectangular blocks shall be laid on an approved bottom. Block shall be at least eight inches thick, constructed of a 4,006 ore test concrete mix, and cured to a 28-day st before installation. (b) Rectangular blocks shall be laid either with mortar joints or filled cores. (c) There shall be at least two coats of 1/4 inch thick concrete plaster placed on the inside of the block tank. There shall be at least two hours elapsed time between • coats. The plaster coat shall start at the bottom course and work up. (2) Circular Block Tanks (a) Circular blocks shall be carefully placed on an approved bottom. Circular blocks shall be at least two inches thick and constructed of a 4,000 psi core test concrete mix, cured to a 28-day strength before installation. (b) There shall be at least two coats of 1/4 inch thick concrete plaster placed on the inside of the block tank. There shall be at least two hours elapsed time between coats. The plaster coat shall start at the bottom course and work up. (3) Sectional Tanks (a) A sectional tank shall have an entire section cast as an integral unit. (b) A sectional tank shall have two or more sections and shall have at least one joint below the level of the outlet in- vert of the tank. (c) Sectional tanks shall have an integrally cast bottom, or . shall be laid on an approved bottom. - 2 - (d) The joint or joints shall be permanently se, .ed so as to be watertight. (4) Bottoms (a) Any tank not having an integrally cast bottom shall not be installed when the water table is closer than three inches to the bottom of the excavation. (b) If the bottom is poured -in -place concrete, it shall be at least four inches thick and extend to at least four inches outside the tank wall. A concrete mix of at least one part cement, two parts washed sand and three parts washed rock shall be mixed before placement in the excavation. (c) If a starter ring is used, it shall be constructed of a 4,000 ps- core test concrete mix, cured to a seven-day strength before installation. It shall extend is least one inch beyond the tank wall, inside and out. A bottom shall be poured of concrete mix defined in Section (b) above. It shall extend at least two inches above the starter ring and shall be at least four inches thick. (d) If a precast bottom is used, it shall be made of a 4,000 psi core test concrete mix, cured to a seven-day strength before installation. It shall extend at least one inch beyond the tank wall, or be cast integrally with the bottom section. (e) sectional tank not having an integrally precast bottom shall have a four -inch thick bottom poured within the tank walls. (5) Covers (a) Any tank cover not integrally cast with the tank shall be so installed that the joint with the tank sidewall is permanently sealed so as to be watertight. (b) All covers shall be so designed and --onstructed as to withstand a minimum of seven feet of saturated earth cover above the tank top. F. Inlet and Outlet•Device Materials (1) Inlet and outlet devices shall be sanitary tees, or baffles constructed of acid resistant concrete, acid resistant fiberglass or plastic. (2) Sanitary tees shall be glued to the inlet or outlet pipes. Baffles shall be integrally cast with the tank, affixed with a permanent waterproof adhesive or affixed with stainless steel connectors, top and bottom. - 3 - i 2. DESIGN All tanks, regardless of material or method of construction, shall conform to the following design criteria: A. The LIQUID DEPTH of any septic tank of compartment thereof shall be not less than 30 inches. A liquid depth greater than six and one-half feet shall not be considered in de- termining tank capacity. B. No tank or compartment thereof shall have an inside horizontal dimension less than 24 inches. C. Inlet and outlet connect -ions of the tank thereof shall be sub- merged by means of ven ., sanitary tees or baffled. D. The space in the tank between the liquid surface and the top of the inlet and outlet baffles or sanitary tees shall be not less than 20 percent of the total required liquid capacity, except that in horizontal cylindrical tanks this space shall be not less than 15 percent of the total required liquid capacity. E. The inlet baffle or sanitary tee shall extend at least six inches but not more than 20 percent of the total liquid depth • below the liquid surface and at least one inch above the crown of the inlet sewer, F. The outlet baffle or sanitary tee and the baffles or sanitary tees between compartments shall extend below the liquid surface a distance equal to 40 percent of the liquid depth except that the penetration of the indicated baffles or sanitary tees for horizontal cylndrical tanks shall be 35 percent of the total liquid depth. They also shall extend above the liquid surface as required in D. above. In no case shall they extend less than six inches above the liquid surface. G. There shall be at least one inch between the underside of the top of the tank and the highest point of the inlet and outlet devices. H. The inlet invert shall be not less than three inches above the outlet invert. I. The inlet and outlet shall be located opposite each other along the axis of maximum'dimension. The horizontal distance between the nearest points'of the inlet and outlet deices shall be at least four feet. 0 • J. Sanitary tees shall be at least four inches in diameter. Inlet baffles shall be no less than six inches or no more than 12 inches measured from the end of the inlet pipe to the nearest point on the baffle. Outlet baffles shall be six inches meas- ured from beginning of the outlet pipe to the nearest point on the baffle. K. Access to the septic tank shall be as follows: (1) There shall be one or more manholes, at least 20 inches least dimension, and located within six feet of all walls of the tank. The manhole shall extend through the cover to a point within 12 inches but no closer than six inches below finished grade. The manhole cover shall be covered with at least six inches of earth. (2) There shall be an inspection pipe of at least four inches diameter or a manhole over both the inlet and outlet devices. The inspection pipe shall extend through the cover and be capped flush or above finished grade. A downward projection of the center line of the inspection pipe shall be directly in line with the center line of the inlet, or outlet device. L. Multiple tanks • (1; Where more than one tank is used to obtain the required liquid volume, the tanks shall be connected in series. • (2) Each tank shall comply with all other provisions of Section I. A. (3) No more than four tanks in series can be used to obtain the required liquid volume. MAINTENANCE SUGGESTIONS - Inspect the tank annually and have the tank cleaned when the scum is 3 inches or less above the outlet baffle and/or when the sludge level is 8 inches or less below the outlet baffle. 3. LOCATION A. The sewage tank shall be placed so that access is convenient for the removal of liquids and accumulated solids. B. The sewage tank shall be placed on firm and settled soil capable of bearing the weight of the tank and its contents. - 5 - • C. Sewage tanks shall be set back the following distances from the features given below: • • Feature Water Supply Well and Buried Water Suction Pipe Buried Pipe Distributing Water Under Pressure Buildings Property Lines The ordinary High Water Mark of: Natural Environment Lakes and Rivers Recreational Development Lakes and Rivers General Development Lakes and Streams Wild River Scenic River Designated Tributaries of Wild, Scenic, and Recreational Rivers Wetlands Minimum Setback Distances (feet) 75' 10' 20' 20' 150* 75* 50* 150* 100* 75* 75' *Required for new developments and where practicable, for existing developments. 4. SURFACE FLOODING Sewage tanks shall not be placed in flood plains delineated by lo0al ordinances adopted in compliance with the Statewide Standards for Management of Flood Plain Areas of Minnesota Minn. Reg. NR 5-93T, or in areas for which regional floodinformation is available from the Department of Natural Resources, except that in areas where ten- year flood information is available from and/or approved by the Department of Natural Resources. - 6 - • III. DISTRIBUTION OF EFFLUENT 1. BY GRAVITY FLOW OVER THE SOIL TREATMENT AREA A. Level Ground Where the elevation difference of the ground surface does not exceed 28 inches in any direction within the soil treatmrit area, the sewage tank eff- ant may be directed to the soil tr atment area through a distribution box. (1) ,The box shall be watertight with a removable cover and shall be constructed of durable materials not subject to excessive corrosion or decay. The minimum inside dimen- sion shall be at least ten inches. (2) The inverts of all outlets shall be at the same elevation as measured from a liquid surface in the bottom of the box. (3) The inlet invert shall be at least one inch above the outlet inverts. (4) The outlet inverts shall be at least four inches above the distribution box floor. • (5) Each drainfield trench line shall be connected separately to the distribution box and shall not be subdivided. When sewage tank effluent is delivered to the distribution box by pump, either a baffle wall shall be installed in the distribution box or the pump discharge shall be directed against a wall or side of the box on which there is no out- let. The baffle shall be secured to the box and shall ex- tend at least one inch above the crown of the inlet flow line. B. Sloping Ground Where the elevation difference of the ground surface exceeds 28 inches in any direction within soil treatment area a drop box shall be installed at the head end of each lateral line. Connec- tions between drop boxes shall re b_, wa' right pipes. (See Figure 2) (1) The drop box shall be watertight and constructed of durable material- not subject to excessive corrosion or decay. The minimum inside dimension shall be at least ten inches, un- less the box is to be used as a valve box. Then each outlet shall have at least eight inches of sidewall space and the side of any outlet shall be at least six inches from any corner. - 7 - • (2) The invert of the inlet pipe shall be at least one inch higher than the invert of the outlet pipe to the next trench. (3) The invert of the outlet pipe to the next trench shall be at least two inches higher than the invert of the outlet pipe of the trench in which the box is located. (4) When sewage tank effluent is delivered to the drop box by a pump, the pump discharge shall be directed against a wall or side of the box on which there is no outlet. (5) The drop box shall have a removable cover either flush or above finished grade or covered by no more than six inches of soil. IV. DRAINFIELD - Final treatment and disposal of all sewage tank effluent shall be by means of soil treatment. 1. SIZING Indicated average percolation rat is 27.5 minutes per inch for the primary site and 23.3 minutes per inch for the alternate site. A. Total a ainfield area is 1002 ft2 • B. Drainfield trench bottom width is 31. C. TOTAL lineal feet of drain tile is 3349. D. This requires 5 laterals of 66' in length. See Figure 1 for typical plac3ment. E. Minimum spacing of laterals is 7.5 feet from center to center. 2. LOCATION A. On slopes in excess of 12 percent the soil profile FiAall be carefully evaluated in the location of the propoe-4d soil treat- ment area and downslope to identify the presence of layers that may cause sidehill seepage. In no case shall. a trench be located within 15 feet of such a layer surfacing on the downslope. B. Bt ;onstruction shall be .limited to areas having natural slopes of less than six percent. C. Any soil treatment area other than seepage pits shall be set back the following distances from the features gl.ven below: • .• Feature Any other water supply well or buried water suction pipe Buried pipe distributing water under pressure Building Property line The ordinary H ter Mark of: Natural Envircir AkeQ and Streams g Recreational Development Lakes and Rivers General Development .akes and Streams Wild River Scenic River Designated Tributari-a of Wild, Scenic, and Recreational Rivers Set back distance in feet 20' 20' 201 150'* 75'* 50'* 150'* 100'* 75' Wetlands 75' *Required for new developments and where practicable, for existing I-velopments. 3. DESIGN AND CONSTRUCTION A. The bottom of trenches and beds shall be at least three feet above the water table or bedrock. B. The bottom of the trench or bed excavation shall --vel. The bott,.i and sides of the trench or 'A excavat-on to the level of the filter material shall be z--arified to remove smears left by the construction equipment and footprints. All loose material shall be removed from the excavation The bottom of the excavation shall not be driven on or walked on aft r scarification. C. When the soil percolation rate at the bottom of the trench or bed is slower than 15 minutes per inch, no vehicle or excava- • tion equipment shall be allowed on the trench or bed area. Excavation shall be by back hoe or other means t-' t allow the equipment wheels o., tracks to remain on the sur :� soil. - 9 - 1 �r • 40 D. There shall be a layer of 12 inches of filter material in the bottom of the trenches and beds placed as shown in Figure 3. E. Distribution pipe used in trenches or beds for gravity flow distribution shall be at least four inches in diameter and constructed of sound and durable material not subject to corrosion or decay or to loss of strength under continuously wet conditions. The ends of each lateral shall be capped. (1) Agricultural drain tile shall be in 12-inch lengths and laid with I./4-inch open joints on grade boards. Ali open joints shall be protected on top by strips of asphalt -treated building paper at least ten inch.:s long and three to six inches wide or by other acceptable means. (2) Perforated plastic pipe shall be laid with one row of - r- forations on the bottom. Perforations shall be at least 1/2-inch in diameter and spaced no farther than 12 inches aF:Art. (3) Other devices may be used to distribute sewage tank effluent over the soil ,'eatme.t area upon approval of the local ad- ministrator of the sanitary ordinance. (4) The distribution pipes shall be laid 19vel or on a uniform slope away from the sewage tank of no more than four inches pe. 100 feet. F. The filter material shall be coverfld with untreated building paper or a two-inch layer of hay or straw or similar, ap- proved permeable materials. G. The trenches or beds shall be backfilled with the excavated material and slightly crowned above finished grade to allow for settling. The backfill shall not be compacted to a density greater than that of the original soil. H. The minimum depth of cover over the distribution pipes shall be at least eight inches. I. The maximum depth of cover over the distribution pipes shall be no more than 36 inches and preferably 24 inches. J. A grass cover shall be catablished over th_- soil treatment area. K. See Figure 3 for further detail. - 10 - Pt-4TP I N T7,. M-#10, 110 LA.HVMAAIlDCNII' 8 d%Kl1> 41 ; I N"v=I I IM-lowm- AP"s -