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HomeMy WebLinkAbout1981-04-14 Septic System Design ReportHAKANSON NAERSA'V ASSOCIATES, Inc* A 0. Box 665 222 Monroe Street Mr. John Laurent 70 Rockwell - 3660 Independence St. Louis Park, Minnesota 55426 Re: Percolation Testing Dear John: professional engineers and surveyors Anoka, Minnesota 55303 April 14, 1981 6121427-5860 At your request percolation testing was performed on the two lots of the proposed Laurent Addition located in part of Government Lot 3 Section 36 Township 118 Range 23, Hennepin County, Minnesota. Standard methods of percolation testing were employed. Elevations are relative to an assumed elevation of 100.0 based at a single spike placed in the east face of the power pole located on the south line of Lot 1 (see enclosed sketch). This report includes: 1. Soil boring logs 2. Percolation test results 3. Testhole location sketch 4. Septic system configuration sketch 5. Discussion and recommendations. The soil boring logs show that, in general, silt loam to silty clay loam surface horizons overlie clay subsurface horizons at the site. Below 1.5 to 2.0 feet depth, mottled and gleyed horizons occur. Soil mottles (spots of contrasting soil color) are accepted indicators of periodic saturation in soils. G1,kyiug (dull gray soil color) forms in soils which are saturated and in a chemi�:a.11y reduced condition for long periods of time. Because the City of Orono requires at least three (3.0) feet elevation difference between the bottom of standard sewage treatment trenches and the water table and/or soil m.,ttling and gleying, the soils at this site are unsuitable for standard methods of on -site waste disposal. It is recommended that an alternate method of sewage disposal, such as the mound (also called the berm) system be utilized at this site. Percolation test results show that measured percolation rates are faster thin the 120 minute per inch minimum rate for mound systems (see below). civil 8 municipal 0 planning 0 soils 0 land surveving Mr. John Laurent - 2 - April 14, 1981 Soil Texture at Percolation Rate Hole Elevation Depth(inches) Bottom of Hole (min/in) #1 99.3 28 Clay loam 0.4 #2 98.1 26 Sandy clay loam 5.0 #3 99.6 27 Silty clay loam 3.5 #4 98.2 22 Sandy clay loam 4.7 #5 97.7 24 Sandy clay loam 6.9 #6 97.5 26 Sandy clay loam 3.9 i #7 99.8 28 Sandy clay loam 5.7 #8 101.0 28 Sandy clay loam to 0.9 sandy loam #9 99.0 32 Sandy loam 6.2 #10 100.5 24 Sandy clay loam 5.0 #11 98.7 26 Sandy clay loam 5.7 #12 97.2 26 Sandy clay loam to 6.4 clay loam The measured percolation rates are somewhat rapid for the texture of the soil materials in which the percolation tests were run. "1 The two mound systems are designed to serve four bedroom houses. The deoigns :j are essentially the same. The size of the rock bed is based on an estimated daily sewage flow of 600 gallons per day. The design infiltration rate of the j medium sand fill of the mound is 1.2 gallons per square foot per day. Therefore, the required rock bed area is 500 square feet. 600 gal/day s 1.2 gal/ft2/day - 500 ft2 A rock bed 10 feet wide by 50 feet long provides the needed area. With 1.5 feet of medium nand below the rock bed and 3:1 sideslopes on the finish cover, the mound skirt covers an area 31 feet wide by 71 feet long. Because: the mound systems will be constructed on slopes, a calculation of the basal area (effective absorption -rea) under the mound is needed. The effective basal area of each mound equals the downslope width multiplied by the bed length (20.5 feet times 50 feet equals 1025 square feet). The required basal area is determined by dividing the loading rate (600 gallons per day) by th- infiltrative capacity of the natural soil (0.74 gallons T)er day for a soil with a percolation late of between 30-60 minutes per inch, silty clay loam to clay loam soits). 600 gal/day r 0.74 gal/ft2/day r 811 ft2 This calculation shows that sufficient effective basal area is provided by the design. The pressure distribution system of the mound consists of Schedule 40 PVC plastic pipe. The supply line and manifold pipe are 2.0 inch inside diameter pipe. The t Mr. John Laurent - 3 - April 14, 1981 supply line should slope back towards the pumping chamber so that it drains after the mound is dosed. The laterals are 1.5 inch inside diameter pipes. The laterals should have 1/4 inch diameter holes drilled at a spacing of 3.0 feet. The laterals should be assembled to the manifold so that the holes point downwards into the rock bed. The distal ends of the laterals should be capped. Also, the last hole in each lateral should be drilled horizontally in the end cap near the crown of the pipe to facilitate air venting. A submersible effluent pump capable of del+vering at least 45 gallons per minute against a total dynamic head of at least "x" feet (as calculated below) should be used. 1. Vertical headloss a. Lot 1 - vertical headloss of approximately 7.8 feet between pump discharge (approx. elev. 93.6) and manifold (approx, elev. 101.4) b. Lot 2 - vertical headloss of approximately 10.5 feet between pump discharge (approx. elev. 91.0) and manifold (approx. elev. 102.5) 2. Friction headloss of 2.36 feet per 100 feet of 2 inch inside diameter PVC supply pipe a. Lot 1 - friction loss of 0.7 feet for 30 feet of pipe b. Lot 2 - friction loss of 2.1 feet for 90 feet of supply pipe 3. Five (5.0) feet to account for losses in distribution system Therefore for Lot 1 and Lot 2 the total dynamic heads are at least 13.5 feet and 17.6 feet, respectively. If any changes in system configuration are made, head - losses should be recalculated. The pump should be rigged with mercury float switches to dose about 150 gallons of effluent to the mound. All electrical connections should be watertight. Also an additional mercury float switch should be installed on a separate circuit to an alarm device to warn of pump failure. The floats should be rigged to allow 600 gallons reserve capacity in the tank. The sole purpose of soils data contained herein is evaluation of soil suit- ability for on -site absorption of septic tank effluent at the test site. Although soil texture and horizonation information and ground water elevation data may be helpful for the setting of basement elevations at this site, we cannot warrant any such interpretations or use of this data for other purposes. Mr. John Laurent - 4 - April 14, 1981 If you have any questions about inform Lion contained in this report, please feel free to contact me. Sincerely, HARA,,NSSO//N ANDERSON ASSOCIATES, INC. W Gary J. Rathbun, Soil Scientist GJR/jkw Enclosures File: 795.01 I I I a A I / I 0 e 3 05' t LOGS Orr SOIL i PR 1 NGS PROJECT: Laurent Percolation Test FILE IJO. 795.01 BORING %THOD: 4" Flight Auger DATE: 3/26/81 DEPTH 0.0 (feet) 1.8 3.0 5.5 7.5 Anrohnlp it Fi cvAirTnu - no a Brown silt loam Grayish brown clay loam with many yellowish brown and red mottles, many gray gleyed areas Grayish brown loath+ coarse sand with many red and yellowish brown mottles, many gray gleyed areas Brown sandy clay with many red and yellowish brown mottles, many gray gleyed.' areas, moist END OF BORING UKUUnU Wj%1zM "W& ppvvulua.=�...�• NMISOII AIUMI ASSOCIAMS, IWC, Rnreholn 52 DEPTH 0.0 _98.9 (feet) I Brown silt loam 1.0 1.5 7.5 Brown clay loam Grayish brown clay loam with man} red and yellowish brown mottles, many gray gleyed spots END LOGS ar SOIL BORINGS PROJECT: Laurent Percolation Test FILE No, 795.01 BuRiNG PIETH= 4" Flight Auger DATE: 3/26/81 DEPTH (feet) 0- 1.. M 6.1 8.( Borehole 43 1. — 97.7 Dark brown silty clay loam Grayish brown clay loam with few yellowish brown and t,d mottles Gray clay loam with many yellowish brown and red mottles, many gray gleyed areas Brown clayey sand with many yellowish brown mottles, wet Grayish brown sandy clay with many yellowish brown mottles, wet END OF BORING GROUND WATER NOT ENCOUNTERED. K"Sal A MI ASSOCIATES, I14C, DEPTH 0.0 (feet) 1.0 2.0 7.5 Borehole #4 R FveTTMI - 100.6 Dark brown silt loam Brown clay loam to sandy loam with depth Grayish brown sandy clay I loam with many yellowish brown mottles, few gray gleyed areas END OF BORING GROUND WATER NnT ENCOUNTERED. BYJr✓ f�t-4^--��ra�e+�+�ar�•so� LOGS ar SOIL WRINGS PROJECT: Laurent Percolation Test FILE NO, 795.01 BARING METHOD: 4" Flight Auger DATE: 3/26/81 DEPTH o . 0 (feet) Dark brown sandy clay loam Brown sandy loam to sandy clay loam with depth Grayish brown sandy clay loam with few yellowish brown and red Taottles, few gray gleyed areas Grayish brown clay loam with many yellowish brown mottles, many gray gleyed areas END OF BORING 0.8 2.0 4.0 7.5 Borehole #5 FI FVATinN - 9Q -A y1%VVAIJ RALGR 111V• L,\VV Vl�1LAGV. RUM AIERSal ASSOCIATES, I.';C. DEPTH o.o (feet) 1.0 2.5 4.0 7.5 Borehole N6 Pi CVATTnm - 9R_2 Dark brown clay loam Brown clay loam Grayish brown clay loam, few yellowish brown mottles, few gray gleyed areas I I Grayish brown clay loam, many yellowish brown mottle' many gray gleyed areas, moist END OF BORING GROUND WATER AT . 81. 3I ; J � � I I I ioA �j x x.i0 9560 l� ';1.Io �JS. ".do f / m 110fr. 4,rnin'!oCRWAC6 W� I 43 L'_V,0,41,VA&6 kVEY FOR: John Laurent i—ZSS. ZO � '- J. ii• L2'00 5CR I PT 1 ON: Lot 2, Block 1, IAURENT ADDITION. is a true and correct representation of a survey of the boundaries ries oifta --- -- �__ n�i tn� i. ,�..,ronn and all visible encroach I! , e � o A 0 � O 0 0 x _ -0-4rvec x IIFJIHX3 P O 8 bt i O 1 NlW�sr�' orF� ,� x �FcveE x C ((��,• � � G v v n S i � A 1 ti 1 � � e 1 � � m � i e° K � k� A R � �e PUMPING Pump should go in a 3rd tank or in a baffled chamber of 2nd tank. The idea is to retain the 2nd tank's capacity for solids retention. An alarm device and reserve capacity equal to one days sewage flow (300 gal. recommended min.) are required. MILL *NO=" [LSOIGE Tl1lJ►711ER'[' sygM LAM;? a INCHES STRAW OR MARSH HAV AND LAVER of RED ROSIN PAPER GRASS COVER 12-24" SAND FILL MAXIMUM SLOPE 3 TO I SANDY LOAM SOIL 6-12" deer r— PERFORATED LATERAL 6 INCHES TOPSOIL TO 15 / _- - '.—_ E. OR DISKED SURFACE CLEAN ROCK q" BEL011 PIPE, 2" OVER DISKED CROSS SECTION A -A PIPE FROM PUMPING CHAMBER as 'I ff I� 1 §" PVc PERFORATED LATERALS ( ( I �� _ k" Holes I every 36" � �EAREA 1 T uj . o 2 v= ��I - --- W INCHES I CLEAN ROCK A 12" DEEPco 0 0 I I 20 INCHE v e INCHES _ SAND 10 FEET—j- nARD 10'min.Y- MAX 10'nin ROC[ R(P Y OVER -ANV Imo. - 1 PLAN VIEW ROCK BED - 3 BR Home - 10'x 40' 4 BR Hone - 10'x 50' 5 BN Home - 10'x 65' 3ARD PILL SHOULD EXTEND 10' C"T FROM AOCX BED ON ALL 3IDE3. QUESTIONS 7 CALL THE SEPTIC SYSTEM INSPECTOR AT 473-7357. CITY OF ORONO GENERAL CONSTRUCTION REQUIREMENTS MOUND DRAINFIELD SYSTEM TO BE USED WHERE: Seasonal perched water table is between 2 feet and 4 feet below surface. Percolation rate in top 12" of soil is faster than 60 MPI. Percolation rate in subsoil but above water table is faster than 120 MPI. Where percolation rate Is 60-120 MPI, depth to groundwater shall be at least 3' and slope must be no more than 3%. Where percolation rate is 30-60 MPI, depth to groundwater shall be at least 2' and slope must not exceed 6%. If percolation rate is faster than 30 MPI, depth to ggroundwater shall be at least 3' and slope must not exceed 6-12%. CONNECTION TO HOUSE House to tanks may be PVC (ASTM D-3034 or better), cast iron or clay tile. PVC should be sand -bedded in flat runs over long distances. No outside air test required but joints must be tight. TANKS Two (2) precast concrete tanks are required. Min. size 1000 gal. and 750 gal.; we recommend 2 1000's. Tanks must have 20" manhole riser to within 12" of final grade, and at least one 4"-6" inspection stack to surface. Baffles must be acid resistant and may be plastic, fiberglass, or precast with tank. DRAINFIELD Mound consisting of 12-24" layer of sand on plowed, chopped, or otherwise scarified natural surface soil. 12" rock bed on top of sand la^er, 10' maximum width X length dependent on water use. Distribution pipe is laid in top 3" of mock. Cover rock bed with straw or hay AND building paper. A layer of sandy loam 6-12" thick should be placed over the covered rock bed and a 6" layer of topsoil then placed over the entire mound. Finished sideslopes to be 3:1 or flatter. Grass cover should be established as soon as possible over the mound area to reduce erosion and aid in evaporation. THE MOST IMPORTANT STEP IN CONSTRUCTING A MOUND IS PREPARING THE NATURAL SOIL SURFACE BY DISC -PLOWING OR CHOPPING WITH A BACKHOE TO A DEPTH OF ABOUT 12". When sand is pushed or dropped onto this loosened raw top- soil (DON'T drive on it), an interface is formed which will allow percolation to occur from the sand into the topsoil. SEE SKETCH ON BACK OF THIS SHEET. DISTRIBUTION The mound must use pressure distribution and requires a pump from the se tic tanks. Distribution must be 1'kk" PVC or plastic with " holes (turned down) every 36". rumping from a 2" manifold, distribution system should be 3 lengths of pipe spaced 40" on center capped at the ends, running the length of the rock bed (see sketch). No drop boxes or distribution boxes are used. 4" PIPE WITH GRAVITY DISTRIB- UTION IS NOT ACCEPTABLE IN A MOUND SYSTEM.