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+ <br />1 <br />RUNOFF CONTRUL FACII�ITIES � <br />Runoff controLfacilities will consist of underground detention tanks designed to detain <br />runoff from t�e developed site and release it to 50% of the existing 2 year runoff, and <br />100%a.o£ the existing runoff for the 10 yeaz and 100 yeaz design storms. The detention <br />tanks ate designed to accommodate the stormwater runoff from the entire site; including <br />the pazking lot, landscaping.and mof tops. Detention volume will be provided by using <br />fovr 95 inch by 67 inch underground pipe arch detention.taaks. Each tank � 100 feet long <br />(access hatch to access hatch). The detention facility will discharge into the existing <br />• storm dtain system through a proposed catch basin neaz the northeast corner of the site. <br />- The following parameters were used to design the runoff control facilities (see appendix): , <br />Soil Alderwood Type C. ^ ,. <br />i / <br />�' � <br />Existing impervioe: area - asphalt 0.15 acres/GN 98 � <br />E�tis�t'n ous azea - rus 8�- ���� ✓ <br />/ <br />Developed impervious area - roof <br />Rainfall_=2.year <br />Rainfall —10 year <br />Rainfall —100 yeaz <br />Existing Tc <br />Developed Tc <br />Existing rnnoff— 2 year <br />Existing runoff-10 year <br />Existing runoff-100 yeaz <br />�.21 aores/ ,_, �/� �, <br />. -�:45�aere��' _� / ( :: <br />, _ cre .CN 86 : � � `� : <br />1.5�".- ---- O ' <br />2.25" <br />3.25" - <br />30 min __ <br />63 min (default minimum) <br />0.1 S cfs <br />C�.33 cfs <br />0.76 cfs <br />See ,�ex���Rp�P <br />� <br />