1982-09-13 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 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 31 and slope must be no more than 34. Where percolation rate is 30-60 MPI, depth to groundwater shall be at least 2# and slope must not exceed 64. If percolation rate is faster than 30 MPI, depth toggroundwater shall be at least 31 and slope must not exceed 6-124. 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 Erade, 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 bad on top of sand layer, 10' maximum width X length dependent on water use. Distribution pipe is laid in top 3" of rock. 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 sidealopes 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 sotic tanks. Distribution must be 1V PVC or plastic with K" holes (turned down) every 36". Pumping 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 boxna are used. 4" PIPE WITH GRAVITY DISTRIB- UTION IS NOT ACCEPTABLE IN A MOUND SYSTEM.