1985-03-07 Septic System Design Report

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i SYSTEM DESIGN FOR JAMES C. LONG LOT 6, BLOCK 2, RINGERSWOOD GRONO, MINNESOTA -7-85 1. Percolation Rate, Type of System. Percolation tests were taken by others. From inf,)rmation supplied, the primary site had a percolation rate of 73 minutes rnr inch, and a high water table at 2 feet. Thus, a pressure mound system sized according to basal width is needed. 2. Proposed Flow Rate. 3 bedrooms - 600 G.P.D. 3. Soil Treatment Area Needed. 600 G.P.D. x 0.83 factor is 500 Sq. Ft. of rock bed area or a bed 10 feet wide by 50 feet long. 4. Septic Tanks and Distribution System. Two septic tanks each of at least 100C gL!Ions are recommended. In add- ition, a third pumping tank or an extra c,ipartment in the second tank will be necled to house the pump required for pressure distribution to the mound system. Distribution to the rock bed is to be through 3 per- forated laterals spaced 40 inches apart. All construction ana materials should adhere to the provisions of the City of Orono. If a future !,athroom in the basement is to be served later, it might be better to use an ejec`- or pump at that time rather than running gravity now and keeping the tanks deep in the ground. The excavation costs would be groater with the deeper tanks and the high water table cou1.1 present greater problems in keeping the tanks watertig't. 5. Mound Dimensions. For a percolation rate of 73 MPI a factor of 5.0 would be used for sizing. This would result in a t-t-il basal width of 10 feet x 5.0 or 50 feet Since the ground slope is less than 3%, both the upslope and doa lope of the mound can be used. Thus, subtracting the 10 foot wide bed, 40 additional feet would be needed for the total upslope and downslope dimensi•.)ns. Also, because of the high water table 2 feet of sand will be needed under the mound making the height 4 feet witL a mi:iimum of 3:1 side -lopes. If there are any other questions, please contact me. Sincerely, PERCOR, INC. Mark S. Gronberg, P.E.