1982-10-27 Septic System Design Report

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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 ()o 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 groundwater shall be at least 3' and slop:. 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. Mitt. 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. DRAI14FIELD Mound consisting of 12-24" layer of sand on plowed, chopped, or otherwise scarified natural surface soil. 12" rock bed on top of sand layer, 10' maximum width X length dependent on water use. Distribution pipe is laid in too 3" of rock. Cover rock bed with straw or hay AND building paper. A layer of sandy loam 0-12" thick shou?d 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 SOII, 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 septic tanks. Distribution must be 1Y' PVC or plastic with 4" holes (turned down) every 36". Pumping from a 2" manifold, distribution system should be 3 lengths of pipe spaced )�O" on center capped at the ends. running the length of the rock bed (see --ketch). No drop boxes or distribution boxes are used. 4" PIPE WITH GRAVITY DISTRIB- UTION IS NOT ACCEPTABLE IN A MOUND SYSTEM.