Laserfiche WebLink
RICE CREEK WATERSHED DISTRICT <br />INFILTRATION WORKSHEET <br />PERMIT NAME: Npf'TV- Copt p";5,',..;,--",!. PERMIT NO. <br />STEP 1: Determine impervious and pervious areas. <br />Note: Include all pervious and impervious areas located in any rights -of -way. <br />(a) Total Site Area <br />(b) Impervious Area <br />x,393 ac <br />/ ac (examples: roads, roofs, parking lots, <br />gravel drives) <br />D. 159 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 arca of permanent pools of ponds or <br />wetlands (see Stormwater Infiltration Guidance Design Parameters). <br />(c) *Effective Pervious Area <br />Note: <br />The effective area available for infiltration must 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 = 55,3 % (d) (d) MUST BE < 800 <br />STEP 3: Determine runoff volume from impervious surfaces generated by median storm <br />of 0.34 inches. <br />/•323 (b) <br />Impervious <br />Area (ac) <br />x 0.9 x <br />0.34 inches x <br />Coefficient . Mpls -S[. Paul <br />Median Storm <br />Rainfall <br />lft <br />12 inches <br />= 0,034 -(e) <br />Volume <br />Needed to be <br />Infiltrated (ac ft) <br />STEP 4: Calculate volume capable of being infiltrated on site within 72 hours. Use <br />infiltration rates listed on page 2 of Stormwater Infiltration Guidance Design <br />Parameters. <br />Saturated infiltration rate,if multiple <br />Type soils = 0.=-7 (1) <br />in/hr <br />0.159 (c) x <br />Effective <br />Pervious) <br />Area (ac) <br />G.25 (1) x <br />Infiltration <br />Rare <br />Corresponding <br />to Soil Type <br />(in/hr) <br />on -site soil types. use most restrictive) ,for <br />for <br />0.03 fir? - 77. —z -0 w O.02 & /'L- <br />0 -7.441 <br />72 <br />Hours <br />1 ft <br />12 inches <br />- O• (g) <br />Volume <br />Infiltrated <br />in 72 Hours <br />(ac-ft) <br />STEP 5: Compare volume generated to volume infiltrated. <br />0.239 (g) MUST BE GREATER THAN OR EQUAL TO 0.03+ (e). <br />RECEIVED <br />SEP 1 1 2000 <br />CITY OF LINO LAKES <br />2 -99 REV <br />