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PERMIT NAME: RICE CREEK WATERSHED DISTRICT INFILTRATION WORKSHEET HA/210 i KAYSTonvi. 57-4 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 B.1.ol (b) Impervious Area *.Oft (c) *Effective Pervious Area ac ac (examples: roads, roofs, parking lots, gravel drives) 2.5CD ac (not a - b) Undisturbed: 0.33 ac Disturbed: 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 area 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 = 0.50 % (d) (d) MUST BE < 80% STEP 3: Determine runoff volume from impervious surfaces generated by median storm of 0.34 inches. + -d8 (b) x 0.9 x 0.34 inches x lft Impervious Area (ac) .Coefficient Mpls -St. Pciul Median Storm Rainfall 12 inches = O. 104- (e) Volume Needed to be Infiltrated (ac ft) STEP 4: Calculate volume capable of being 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 Q soils = 0.25 (f) in/hr Sr. (c) x 0.15 (f) x 72 x Effective Pervious) Area (ac) Infiltration Rate Corresponding to Soil Type (in1lir) Hours 1 ft 12 inches = 3. a4 (g) Volume Infiltrated in 72 Ho (ac STEP 5: Con are volume generated to volume infiltrated. -19--(g) MUST BE GREATER THAN OR EQUAL TO 0.10 ( .vtf.•1*eY•y..,f tli....a .• • JUN 152000 )r,IT'Y OF LINO LAKES 2 -99 REV