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Lots 80,81, Sarakumett, Con t'd. <br /> a. design storm of 7 inches in 24 Fours .(Type II rainfall <br /> as defined by SGS) and <br /> b. standard Soil Conservation Service (SCS) methods set <br /> forth in Technical Release No. 55, Urban Hydrology for <br /> Small Watersheds and Section 4 of the SCS National <br /> Engineering Hydrology Handbook. <br /> The same criteria applies to land which is isolated but is <br /> Subject to flooding. In the case of isolated land, total runoff <br /> volume is the unmown quantity to be determined, <br /> Arrow Engineering, Inc. Calculation <br /> The plan accompanying the computations does not show sufficient <br /> contouring beyond the property lines to confirm the extent of the <br /> contributing watershed to lots 80 and 81. The penciled blue line <br /> on the plan appears to fall short of three spot elevations shown <br /> near- the end of Noisy Mole Road. It also appears from the HSGS <br /> quadrangle and the plan supplied that the contouring of lots 1-5 <br /> and the land beyond may have been left out of the contributing , <br /> area. In order to complete an effective calculation, all of the <br /> land which could contribute runoff must be included.- <br /> The calculations are also based on the Rational method for <br /> computing runoff. This method, widely accepted in engineering <br /> circles, is not the method accepted or required by 310 CMR 10.57. <br /> To get results which are consistent with the requirements of <br /> the wetlands regulations and definitions, the Soil Conservation <br /> Service (SCS) method of calculating, runoff should be employed. <br /> The plan shows the location of proposed well and leaching <br /> areas for lots 80 and 81. Title 5 of the State Environmental <br /> Code requires the compliance with the Wetlands Act in terms of <br /> setback distances from wetlands and watercourses. "These setbacks <br /> should be reviewed along with the 100 year-flood..line for compl- <br /> iance. <br /> Before-making a final determination that elevation 44.3 i <br /> the extent of the loo year flood, as Arrow Engineering has sugg- <br /> ested, the Commission should have the questions of watershed <br /> Bruits and methods of computation addressed by the applicant's <br /> engineer. <br /> Very t ly yours, <br /> Charles L. Rowley, PE, RLS <br />