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<br />Rice Creek Watershed District <br /> <br />INFILTRATION WORKSHEET <br /> <br />PERIMT NAME: MI.4LTI W~B CDNVf.R.,',.j6 <br /> <br />PERMIT NO. <br /> <br />D7-cRl <br /> <br />STEP I: Determine impervious and pervious areas. <br /> <br />Note: Include all pervious and impervious areas located in any rights-of-way. <br /> <br />(a) Total Site Area: <br /> <br />'3,27 <br /> <br />ac <br /> <br />(b) Impervious Area: 1."'2.'1 ac (examples: roads, roofs, parking lots, gravel drives) <br /> <br /> <br />(c) 'Effective Pervious Area: 0,076 ac [not (a) - (b)J <br /> <br />Undisturbed: <br /> <br />ac Disturbed: 0.07'- <br /> <br />ac <br /> <br />* Only use horizontal component of surface area which is subject to intermittent prolonged wetting. <br />Do not include area of permanent pools of ponds or wetlands (see Stormwater Infiltration Guidance <br />Design Pararneler5). <br /> <br />Note: The effective area available for infiltration must be capable of receiving the runoff from <br />impervious surfaces. Pervious "islands" located above adjacent parking lot surfaces, for example, <br />will not be credited. <br /> <br />STEP 2: Demonstrate 0/1) imperviousness for the site. <br /> <br />[(b) -;- (a)] x 100 ~ 3'1.'-/ <br /> <br />_%(d) <br /> <br />(d) MUST BE'; 80% <br /> <br />STEP 3: Determine runoff volume from impervions surfaces generated by median storm of 0.34 inches, <br /> <br />1.2."/ (b) <br />Impervious <br />Area (acres) <br /> <br />x 0.9 x <br />Coefficient <br /> <br />0.34 inches x <br />Mpls-St. Paul <br />Median Stann <br />Rainfall <br /> <br />I foot <br />12 inches <br /> <br />0,033 (e) <br />Volume needed <br />to be infiltrated <br />(acre-feet) <br /> <br />STEP 4: Calculate volume capable of being infiltrated on site within 72 hours. Use infiltration rates listed on <br />page 2 of Storm water Infiltration Guidance Design Parameters. <br /> <br />Saturated infiltration rate (if multiple on-site soil types, use most restrictive) for <br />Type C soils ~ 0, I 0 _ (I) <br />incheslhour <br /> <br />O.07b (c) x <br />Effective <br />Pervious <br />Area (acres) <br /> <br />0, /0 (I) x 72 x <br />Infiltration Hours <br />Rate <br />Corresponding <br />to Soil Type <br />(inches/hour) <br /> <br />I foot <br />12 inches <br /> <br />0,01.{(, (g) <br />Volume <br />infiltrated <br />in 72 Hours <br />(acre-feet) <br /> <br />STEP 5: Compare volume generated to volume infiltrated. <br /> <br />0,01.{ b <br /> <br />(g) MUST BE GREATER THAN OR EQUAL TO 0.033 <br /> <br />(e). <br /> <br />2-99 REV <br />