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DETENTION ANALYSIS <br /> Total Site Area = 0.27 Acres <br /> Study Area = 0.27 Acres <br /> From the NRCS of Snohomish County, the majority of the site contains Alderwood Soils <br /> that has a hydrologic classification of"C". <br /> Existing Conditions: <br /> Study Area = 0.27 Acres <br /> Existing Basin Area = 0.27 Acres <br /> Refer to the Existing Basin Map attached later in this section for more details. <br /> Developed Conditions: <br /> Study Area = 0.27 Acres <br /> Developed Basin Area= 0.27 Acres <br /> Impervious area: <br /> Roof area =0.07 Acres ( 3,157 SF) <br /> Driveway =0.03 Acres ( 1,556 SF) <br /> Sidewalk = 0.01 Acres ( 224 SF) <br /> Total Impervious =0.11 Acres (4,937 SF) <br /> Pervious area=0.27 Acres - 0.11 Acres= 0.16 Acres <br /> Refer to the Developed Basin Map attached later in this section for more details. <br /> Infiltration Drywell Sizing: <br /> Medium Sand Designation: 90 cf/ 1,000 SF impervious <br /> 4,937 / 1,000=4.937 <br /> 4.937 x 90 =444.33 <br /> Drywell Volume Required=444.33 cf <br /> Drywell Volume Provided=452.39 cf <br /> A 6' deep, 12' 0 drywell will be provided. <br /> Insight Engineering Co. - Stormwater Site Plan 6/22/2022 <br /> -26- <br />