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TO: Jeanne A. Mabusth, Zoning Administrator FROM: Michael P. Gaffron, Assistant Zonin3 Administrator DATE: August 19, 1985 SUBJECT: 1956 Mrs. Philip W. Pillsbury - Approval of Septic_ System Plans I have reviewed the soil testing information and design submitted fr.r the proposed septic system to serve the new house on this pro- perty. With slight modifications, this proposed system will be ac- ceptable and will meet minimum code standards. I would 1 ike to brief ly address the proposed system design and the proximity to water table. The soi 1 borings indicated a surface layer of 2' of dark loamy sand with a perc rate averaging 3.5 minutes per inch. The water table at this site appears to be concurrent with the lake le•✓el, and soil boring logs and my own soil boring indicate the highest visible sign of past water tables is at about 3'6" below the surface. It the lake level rises to it's highest recorded 'Level (930.5' in the 1930's) the bottom of trenches should be aL least 933.5' or higher, which coincides cl)srrly with the existing ground surface. Jim Mahady of the MCWD informs me that the 10-year flood elevation for Lake Minnetonka has been estimated at 930.0 and the 50- year flood at 930.6; but he tells me also that these numbers are speculative aid may over -estimate the flood levels. Also, there is no estimate as co how long the lake level would be this high if such flooding was to occur. The proposed system inc.' l udr,s a lift station in the heated garage area, discharging to two septic tanks at a higher elevation. Because the perc rate is just below 5 mpi, the 4 trench-�-s must be loaded serially (with drop boxes) rather than with a single distribution box. This modification is required by WPC - 40 and will allow the build up of biomat to occur sooner, the biomat acting to slow the effluent flow through the soil to an unsaturated flow so that treat- ment can occur. The second modification is to increase the length of the trenches from 42' to 50' so that the drainfield meets the 600 s.f. minimum required by Orono code for any house. This may require slightly relocating the second tank which should not be a problem. Note that the existing driveway is paved and is likely underlain by gravel to some depth. A portion of the drainfield is proposed for this area. The gravel and pavement must be removed end replaced with a loamy sand material simi lar to the surroundin i top soil prior to placement of the s&ndy loamy t 1 1. A secondary drainfield site F-•xists directly nor'h of the proposed driveway, where similar soil and water conditions exist. 1 would r-commend approval nf the lot arf.�,i ,ini ViAtr, v,,rian.es r equer ted .