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Sent By: Glenn Rehbein Co; <br />6127846001; Mar -13 -01 9:53AM; <br />RICE CREEK WATERSHED DISTRICT <br />INFILTRATION WORKSHEET <br />PERMIT NAME: Sr :1' • 14z f ` PEItivin NO. <br />STEP 1: Determine impervious and pervious areas. <br />Note: Include all pervious and impervious areas located in any rights-of -way. <br />34. SS <br />Page 2/2 <br />(a) Total Site Area ae <br />(b) Impervious Area /d•8 ac (examples: roads, rocfs, parking lots, <br />gravel drives) <br />(c) *Effective Pervious Area O, es" ac [not (a) — (b)] <br />Undisturbed: ac Disturbed: ac <br />* Only use horizontal component of surface area which is subject to intermittent <br />prolonged wetting. Do not include area of permanent pools of ponds or <br />wetlands (see Stormwater Infiltration Guidance Design Pe.rameters). <br />Note: The effective area available for infiltration trust be capable of receiving <br />the runoff from impervious surfaces. Pervious "islands" located above <br />adjacent parking lot surfaces, for example, will not be credited. <br />STEP 2: Demonstrate % imperviousness for the site. <br />[(b) + (a)) x 100 = 2 % (d) (d) MUST BE 5 80% <br />STEP 3: Determine runoff volume from impervious surfaces genera <br />of 0.34 inches. <br />10.1 .(b) x <br />Impervious <br />Area (ac) <br />0.9 x 0.34 inches x <br />Coefficient Mpla -St. Paul <br />Median Storm <br />Rainfall <br />lft <br />12 inches <br />by median storm <br />0.2k (e) <br />Volume <br />Needed to be <br />Infiltrated (ac -ft) <br />STEP 4: Calculate volume capable of being infiltrated on site w!thin 72 hours. Use <br />infiltration rates listed on page 2 of Stonnwater Infiiiraaon Guidance Design <br />Parameters. <br />Saturated infiltration rate (if multiple on -site soil types, us: most restrictive) for <br />Type ! soils = o._ (E) <br />in/br <br />v, PS (c) x <br />Effective <br />Pervious) <br />Area (ac) <br />0.3 .. (1) x <br />h{fiitration <br />Rate <br />Corresponding <br />to Soil Type <br />(') <br />72 <br />Hours <br />1ft <br />12 inches <br />STEP 5: Compare volume generated to volume infiltrated. <br />(g) MUST BE GREATER THAN OR EQUAL TO <br />I.S3 <br />(g) <br />Volume <br />Infiltrated <br />in72Hours <br />(ac f t) <br />(e). <br />2-99 REV <br />