1985-05-20 Septic System Design Report

Home Browse Search

CITY OF ORONO GENERAL CONSTRUCTION REQUIREMENTS MOUND DRAT_NFIELD SYSTEM TO BE 1'3ED 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 groundwater shall be at least 3, and slope must not exceed 6-12%. CONNECTION TO HOUSE House to tanks may be PVC (ASTM P-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 h,ve 20" manhole riser to within 12" of final grade, and at least one 4"-6" inspection stack to surface. Baffles .crust he 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 layer, 10' maximum width X length dependent on water use. Distribution pipe is laid in top 3" of rock. Cover rock bed with s„raw 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 sntire mound. Finished sideslopes to be 3:1 or flatter. Grass cover should be establishes as soon as possible over the n.ound 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 3ACKHOE TO A DEPTH OF ABU%;T 12". When sand is pushed or dropped onto this loosened raw top - boil (DON'T drive on it), an interface is formed which will allow percolation to occur from the sand into the topsoil. SEE "WETCH ON BACK 0? THIS SHEET. DISTRIBUTION The mound must use pressure distribution and requires a pump from the se tic tar. s. Distribution must be 1ln" PVC or plastic with �" holes (turned down) every 36". Pumping from a 2" manifold, distribution system st.ould 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 A17CEPTABLE IN A MOUND SYSTEM.