01/31/2001 Env Bd Packet - Laserfiche WebLink

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PERMIT NAME: RICE CREEK WATERSHED DISTRICT INFILTRATION WORKSHEET So ne I j naff PRoTTCT IoN PERMIT NO. • STEP 1: Determine impervious and pervious areas. • Note: Include all pervious and impervious areas located in any rights -of -way. (a) Total Site Area 2.O (b) Impervious Area Li. 246 ac (examples: roads, roofs, parking lots, ' gravel drives) (c) "Effective Pervious Area 0.15 / ac (not a — b) Undisturbed: 1.95 ac Disturbed: S. ZS 5 ac * Only use horizontal component of surface area which is subject to intermittent prolonged wetting. Do not include area of permanent pools of ponds or wetlands (see Stormwater Infiltration Guidance Design Parameters). Note: The effective arca available for infiltration must be capable of receiving the runoff from impervious surfaces. Pervious "islands" located above adjacent parking lot surfaces, for example, will not be credited. STEP 2: Demonstrate % imperviousness for the site [(b) + (a)] x 100 = 58.5— % (d) (d) MUST BE < 80% STEP 3: Determine runoff volume from impervious surfaces generated by median storm of 0.34 inches. 11 "216 (b) 0.9 x - 0.34 inches x lft 12 inches Impervious Coefficient Mpls -St. Paul Volume Area (ac) Median Storm Needed to be Rainfall Infiltrated (ac ft) 0.10 (e) STEP 4: Calculate volume capable of tieing infiltrated on site within 72 hours. Use infiltration rates listed on page 2 of Stormwater Infiltration Guidance Design Parameters. Saturated infiltration rate (if multiple on -site soil types, use most restrictive) for Type $ _ soils = a 2-5 (f) in/hr 1 ft 0! (c) x Q 2S 72 0.2-0 12 inches (a) Effective Infiltration Pervious) Rate Area (ac) Corresponding to Soil Type (in/hr) Hours STEP 5: Compare volume generated to volume infiltrated. O. 2.01 (g) MUST BE GREATER THAN OR EQUAL TO 0.10$ Volume Infiltrated in 72 Hours (ac ft) • RECE :yEO e). jP099 till001 CM)'Y OF LI O LAKES