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2 . We agree that the slope under the mound is about 11. 5% as your letter indicates. We have used a Lotus 123 spreadsheet which we created to calculate mound quantities. This worksheet is based on assumptions for a conventional mound. In the unusual case of a double mound which was dictated on this site for reasons of very limited space, the worksheet is of little use in calculating mound dimensions but it does calculate pump details and rock bed areas and some other quantities correctly. We entered such data as was necessary for the spreadsheet to calculate those quantities that it could. The underlying slope was not one of these quantities so it was left as it was from the last job calculated. We then proceeded to size the mound based on space available and then used a calculator to check basal area and other "custom" aspects of this design. In retrospect, it would have been helpful if we had crossed out the portion of the form that we didn't use to avoid causing you confusion and a written record of our check of basal area and mound dimensions would have also been helpful in that regard. �„ We measure a "wetable interface" of 860 square feet :`- under our mound. The acceptance rate of the rock bed • is 1.20 gallons per day per square foot and the acceptance rate of the 13mpi underlying soil is 0.79 '� gpd/ft2 . Dividing these rates yields a 1.52 basal '`' \r width ratio and multiplying that ratio times the rock `a �� bed area of 380 square feet we obtain a required '� C "wetable interface" of 577 square feet. This provide � � �'� about a 50% overdesign but because of possible - variation in the percolation rates and steepness of y � C� some portions of the underlying site we felt that it � was no t a dvisable to reduce the size of the mound. � � � � 3 . We used all percolation test results for �� determination of the average percolation rate which were taken at a depth appropriate for that purpose. Such tests are to determine the acceptance rate of the sand soil interface and are taken at a depth of about a foot. Tests 1, 3, and 5 were taken at 14 inches and yielded rates of 21, 8, and 11 minutes per inch respectively which averaged result in a design rate of 13 mpi.