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HomeMy WebLinkAbout1978-09-28 Septic System Design Reportc_ )-A41 %L11 77 ��� - ly L T 73 s s EA. i KXW A A960CIATE9 l�Ed2�E Pam• JPCXSoN oec*AO, r tlI ---RAPOLIB•MIIrldESO�fA C iIw rleLD P Hof Dr?.AIr1FiEl.p � g �`�"n1aRx�tloi 1 UNES %jbPI uW OF i C>J gE `A+ ?D R,�,E►1I) .-11'T-44 . L>4 IUSC N-I' . L4r�*"fio►1 of PUrIMtJls �w 1P-*-t- P-4A>7 e'EYTic, a>JL)Il r IN, oPoN F ol-L ItX,^Tjc)o Of,-' �� (� EON Tcw) aoc_w %Er' • Yet 0 e yy C . V . SNtib OZJo2 i t it> PuripNl'. C+*mfAl- E-. l.tiOl1T '^tJ SITE. En. MKOK i ASSWAM `. -fT -11� MYDAOLO(iMT3 lAb(x JK4CSC" c7Z�v, r1,J, I �A "-MWWWTA �30 ILPlN hE l.p i%,ov, Vi PA F►Zor1 PUr-PNL, cNwlbU LOCO q►.LL4> to Fli PIN V C,k PJ1 F-+JZ o K. (Z) Icy INU.OtA 4 k- �F f flILDfALO %-JEP �--/- eeOPOF . NbR,1F� sc kLrr. I', l.o L E.A. WAM a ASSMATES S6Pf "I& P►. JPC,KSdtJ JO, MrJ. HYOROLOOISTS-EI�K tem WEAPOL*-MM#ESOTA °�Z' 161.0 2400, (N I 116,;1 1 portp4 FiEt,D lox h x � kq PL 4a2.s •PI �2 s�3 shti — SbtANp',(tj' E. `m I,oc I,ES"�JZ Lop.r'1 Z To 1. L4;ls e 1 I to To Z 90 I ?� , �Zeyb "111,.0, AOa.A-Joco SILTY C4>,Y LOW ZTd 1,re Ir � ioN S1 t-cx.,o.Ti oN r Pr"' EA, H CM & ASOOCIATES SE r lb HYDROU)QIM- l�Eoel�£ �•. JPG��+J oQ,v�1^�, � i►..1. IYM�EAPOI.IS-�AM�E�OTA I o� TABLE 1 PERCOLATION RATES AND DEPTH TO THE WATER TABLE Percolation Rate Depth to the Hole (Minutes/Inch) Water Table (Feet) P1 5.2 - P2 15.0 - P3 5.0 - P4 7.5 - P5 16.5 - P6 5.5 - Sbl - 3.0 Sb2 - 3.5 3b3 - 3.5 Sb4 - 3.0 SOIL BORING 1 - Depth (Feet) 0.r' - 0.5' G - 1.2' - 4.0' 4.0' - 8.0' TABLE 2 SOIL LOGS Material Black loam Black silty clay loam Yellowish brown silty loam, mottled with gray clay at 3.01. Yellowish brown silty clay The water level was recorded at a depth of 3.711, 24 hours after the hole was augered. SOIL BORING 3 - SOIL BORING 2 - Depth (Feet) 0.0' - 0.5' 0.5' - 2.5' 2.5' - 8.0' Material Black loam Black silty clay loam Yellowish brown silty clay, mottled with gray clay at 3.5'. The water level was recorded at a depth of 4.66', 24 hours after the hole was augered. SOIL BORING 4 - Depth (Feet) Material Depth (Feet) 0.0' - 1.0' Black loam 0.0' - 3.0' 1_0' - 2.5' Black silty clay loam 3.0' - 4.0' 2.5' - 3.0' Grayish brown silty 4.0' - 5.0' clay loam 3.0' - 3.5' Dark Yellowish brown 5.0' - 6.0' silty clay loam 3.5' - 8.0' Grayish brown silty 6.0' - 8.0' clay, mottled with gray clay at 3.5'. Material Black clay loam Gray clay Olive brown silty clay Reddish brown sandy clay Yellowish brown sandy clay The water level was recorded at a The water level was recorded at a depth of 4.17', 24 hours after the depth of 4.83', 24 hours after the hole was augered. hole was augered. SPECIFICATIONS FOR PROPOSED ON -SITE SEWAGE DISPOSAL SYSTEM MOUND: PRESSURE DISTRIBUTION LOCATION: George A. Jackson Lot 4, Block 1, The Nursery, Orono, Minnesota Job Number 11-78-47 DATE: September 12, 1978 I. SEWAGE TANK - TWO 1000-gallon LIQUID CAPACITY tanks, IN SERIES, manufactured 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. 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 4,000 psi core test concrete mix, and cured to a 28-day strength 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 irzh 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 sealed 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 psi core test concrete mix, cured to a seven-day strength before installation. It shall extend at 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) A sectional tank not having an integrally precast bottom shall have a four -inch thick bottom poured within the tank walla. (5) Covers (a) Any tank cover not integrally cast with the tank shall be so installed that the joint with the tank sidewall is perntan�-!ntly sealed so as to be watertight. (b) All covers shall be so designed and constructed 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 - 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 di-ension less than 24 inches. C. Inlet and outlet connections of the tank thereof shall be sub- merged by means of vented, 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 cylindrical 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 devices shall be at least four feet. - 4 - • J i 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 lea."t dimension, and located within six fee: of all walls of the tank. The manhole shall extend throu,lh 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 pine 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 fini3hed 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 cf 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. Sew I(je t,inks shall be set. back the following distances from the features given below: Feature Minimum Setback Distances (f`-t) Water Supply Well and Buried 75' Water Suction Pipe Buried Pipe Distributing 20' Water Under Pressure Buildings 20' Property Dines 20' The ordinary High Water Mark of: Natural Environment Lakes 150* and Rivers Recreational Development 75* Lakes and Rivers General Development Lakes 50* and Streams Wild River 150* Scenic River 100* Designated Tributaries of 75* Wild, Scenic, and Recreational Rivers Wetlands 75' *Regiii.L for new developments and where practicable, for existing developments. 4. SURFACE FLOODING Sewage tanks, shall not be placed in flood plains delineated by local ordinances adopted in compliance with the Statewide Standards for Manaccment of Flood Plain Ar.cas of. Minnesota (Minn. Reg. NR85-93), or in areas for which regional flood information 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 - 4 II. PUMPING A 600-gallon capacity tank, placed in series with the sewage tank, shall be manufactured and installed in compliance with the following specifications. See Figure 1 for location. 1. PUMPING CHAMBER A. The pumping chamber shall be watertight and constructed of sound and durable materials not subject to excessive corrosic- or decay. B. There shall be one or more manholes, at least 20 inches least dimension and preferably located directly above the dosing devi. The manhole shall extend through t,ie dosing chamber cover to final grade and shall be so constructed as to pre- vent unauthorized entry. 2. PUMPS FOR PRESSURE DISTRIBUTION A. A pump shall deliver the dose to the soil treatment area. B. The pump discharge capacity shall be at least 30 gallons per minute for a three -bedroom or smaller dwelling and an addi- tional ten gallons per minute for each bedroom above three. C. The pump shall be cast iron or bronze fitted and with stain- less steel screws or constructed of other sound, durable and corrosion -resistant materials. D. The quartity of effluent delivered for each pump cycle shall be no more than 25 percent of one day's sewage flow or 200 gallons, whichever is greater. E. The pump discharge head shall be at least five feet greater than the head required to overcome the pipe friction loss and the elevation difference between the pump and the distribution system. F. An alarm device shall be installed to warn of pump failure. For dwellings, there should be reserve storage volume equal to one day's sewage flow based on 150 gallons per bedroom. III. DRAINFIELD 1. LOCATION A. Mounds shall be i,-.:ated on flat areas or crests of slopes whenever possible. B. Mounds shall not be located on natural slopes of more than 3 percent if the percolation rate in all layers of natural or fill soil to a depth of at least 24 inches below the sand layer of the mound is slower than 60 minutes per inch. - 7 - C. Mounds shall not be located on natural slopes of more than 6 percent if the percolation rate is slower than 30 minutes per inch in all layers of natural or fill soil to a depth of at least 24 inches below the sand layer of the mound. D. Mounds shall not be located on natural slopes exceeding.12 percent tinder any soil percolation rate condtditions. E. Mounds shall not be located on any soil where the percolation rate in any layer of natural or fill soil to a depth of at least 24 inches below the sand layer of the mound is slower than 120 minutes per inch. 2. CONSTRUCTION EQUIPMENT , rubber -tired tractor may be used for plowing or disking to prepare the soil surface but in no case shall a rubber -tired tractor be uses after the surface preparation is completed. A crawler or track -type tractor shall be used for mound const..:uc- tion. 3. SOIL SURFACE PREPARATION A. The discharge pipe from the pump to the mound area shall be installed prior to soil surface preparation. The trench excavated to install the discharge pipe shall be carefully r3ckfilled and compacted to prevent seepage of effluent. B. The total area selected for the mound, includii,g that under the dikes, shall be roughened in order to thoroughly break up any existing sod layer and to provide a suitable transition zone between the original soil and the sand layer of the mound. The area shall be roughened only when the moisture content of the soil 8 inches below the surface is drier than the plastic limit. Plastic limit is the soil moisture content below which the soil may be manipulated for purposes of installing a soil treatment system, and above which manipulation will cause compaction and puddling. If. a fragment of soil can easily be rolled into a w.re 1/b inch in diameter, the moisture content is above the plastic limit. if the soil is dry t_ugr to be friable and falls apart when rolling it into a wire, the moisture content is below the limit, and the soil may be man- ipulated. The standard method of determining the plastic limit is specified in American Association of State Highway Officials (AASHO) Desionation: T 90-61. ft C. Surface preparation or roughening may be performed with a mold board plow, a disk plow, or a backhoe using only the teeth. Mold board plow furrows shall be at least 8 inches deep, shall be thrown upslope and shall run perpendicular to the slope. There shall be no deadfurrow under the mound. Disking may be used for surface preparation as a substitute for mold board piowinq in soils having percolation rates faster than 15 minutes per inch (sandy loam) in the top 8-inch depth. backhoe teeth may be used to rougLen the soil surface and break up the sod layer. Care must be taken so as not to compact or puddle deeper soil layers. In no case shall any surface soil be excavated and removed from the area. D. Mound construction shall proceed immediately after surface preparation is completed. Every effort should be taken to prevent rain from falling on the prepared soil surface. 4. SIZE (See Figures 2 and 3 for layout and details) A. The bottom area of the filter material (rock) was sized on the basis of 0.83 square feet per gallon of waste per day, yielding 500 square feet. B. In no case shall the width of the filter mate ial (rock) in a single bed exceed 10 feet. 5. CONSTRUCTION MATERIALS AND PROCEDURES A. A minimum. of 12" of soil defined as sand she: be placed where the filter i.iaterial is to be located. ti crawler tractc�- with a blade or buck,,t shall be used to move the sand into place. At least 6 inches of sand shall be kept snder the tracks to minimize compaction of the plowed layer. The sand layer upon which the filter material is placed shall be level. B. Sand is defined as a soil texture composed by weight of at leact 25 percent of very coarse, coarse, and medium sand varying in size from 2.0 to 0.25 mm, less than 50 percent of fine or very fine sand ranging in size between 0.25 and 0.05 mm, and no more than 10 percent of particles smaller than 0.05 run. C. A depth of at least 9 inches of filer material (rock) shall be placed on the sand layer prior to installing the distri- bution pipe. - 9 -- 0 D. Filter material is defined as clean rock, crushed igneous rock or similar insoluble, durable and decay -resistant material free from dust, sand, silt, or clay. The size shall range from 3/4 inch diameter to 2-1/2 inch diameter. E. Effluent shall be distributed over the filter material by 1-1/4 inch diameter perforated pipe under pressure. Per- foration holes shall be 3/16 inch in diameter drilled in a straight line along the length of the pipe. Hole spacing shall be 36 inches. Holes shall be drilled straight into the pipe and not at an angle. A sharp drill shall be used and any burrs in the inside of the pipe shall be removed. The perforated pipe laterals shall be installed level with the perforations downward. F. The perforated pipe laterals shall be connected to a 2-inch diameter manifold pipe and shell have their ends capped. The laterals shall be spaced no further than 40 inches on center and no further than 20 inches from the edge of the filter material. Laterals shall be no longer than 50 feet. G. The manifold pipe shall be connected to the supply pipe from the pump. The manifold shall be sloped toward the supply pipe fx)m the pump. H. At least 2 inches of filter material shall be placed over the lateral pipes. I. Straw or marsh hay to an uncompacted depth of 3 to 4 inches or untreated building paper shall be placed over the filter material. J. Construction vehicles shall not be allowed on the filter material until backfill is placed. K. Sandy loam soil shall be placed on the filter material to a depth of one foot in the center of the mound and to a depth of six inches at the sides. L. Six inches of topsoil shall be placed on the fill material over the entire area of the mound. A grass cover shall be established over the entire area of the mound. M. No shrubs shall be planted on the top of the mound. Shrubs may be placed at the foot and side slopes of the mound. N. Side slopes of 4 feet horizontal to 1 foot vertical (4:1) are suggested for the dikes of the mound. This gentle slope will allow easy mowing of the grass cover. If area is lim- ited, steeper side slopes of 3:1 can be used. But in no case shall the dike slope be steeper than 3:1. The soil material at the toe of the dike should be slightly 1 ;s - 10 - permeable or somewhat tighter than.the natural soil below the mound. This can be accomplished by selecting a finer soil or by compaction. O. Whenever mounds are located on slopes a diversion shall be constructed immediately upslope from the mound to inter- cept and divert runoff. P. A 4" inspection well shall be provided for and should be placed in the center of the field and capped flush with the ground. Q. Any soil treatment area shall be set back the following distances from the features given below: Feature Set Back Distance In Feet Water supply well less than 50 feet deep and not encountering at least ten feet of imp"rvious material 100, Any other water supply well or buried water suction pipe 75' Buried pipe distributing water under pressure 20' Building 20' Property lines 20' The ordinary high water mark of: Natural Environment Lakes & Streams 150* Recreational Development Lakes 75* General Development Lakes & Streams 50* Wild River 150* Scenic River 100* Recreational River 75* Designated Tributaries of Wild, Scenic, and Recreational Rivers 75* Wetlands 75' *Required for new developments and where practicable, for development.