1985-7969 - general permit - Laserfiche WebLink

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r , CITY OF ORONO GENERAL CONSTRIICTION REQUIR�iTS MOUND DRAINFIE�D SYSTIIK 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 t� 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 2t and slope mus� not exceed b�. If percolation rate is faster than 30 MPI, depth to groundwater shall be at least 3t and ^ slope must not exceed 6-12�. CONNECTION TO HOIISE � : 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 �al . ; we recommend 2 1000� s . Tanks must have 20" manhole riser to within 12" of final grade, and at least one !}"-6" inspection stack to � surface . Baffles must be acid resistant and ma� be plastic , fiberglass, or precast with tank. DRAINFIELD . Mound consisting of 12-2L�" layer of sand on plowed, chopped, or otherwise scarified natural surface soil . 12" �ock bed on top of sand layer, 10 � maximum width X len�th 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 sidesYopes 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 IlKPORTANT STEP IN CONSTRIICTING 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 �" PVC or plastic with 4" holes (turned down) every 36" . Pumping from a 2" manifold, distribution system ahould be 3 lengths of pipe spaced 40" on center capped at i�he ends, runnin� the len�th of the rock bed (see sketch) . No drop boxes or distribution boxes are used. L�." PIPE WITH GRAVITY DISTRIB- UTION IS NOT ACCEPTABLE IN A MOUND SYSTE�I.