10330 4TH AVE W 2016-01-01 MF Import

South Pointe Assisted Living Facility. Storm Drainage Report. DRAINAGE CRITERIA The calculations for sizing the foilowing described storm water facilities are based on the following criteria: Detention Storage: 100 ye;�r�,o ye °U24 hou�pre-de� oped release 10 year, 24 hour developed storm with 10 year, 24 hour pre-developed release 2 year, 24 hour developed storm with '/Z - 2 ye�r, 24 hour pre-developed release Existing Conditions: Proposed Conditions: Soil Type: SCS Curve Number: (Developed Conditians) Pervious area = 0.48 Acres Impervious area = 0.07 Acres Total area = 0.55 Acres Pervious area = 0.22 Acres Impervious area = 0.33 Acres Total area = 0.55 Acres SCS Group C Pervious C�: 86 Impervious C�: 98 RUNOFF CONTROL In compliance with the City of Everett Design Standards and the Washington State Department of Fisheries, surtace runoff will be controllad by means of an on-site faciliry. The on-site drainage runoff control facility was designed to control the discharge of peak runoff rates from the pr�ject siie under new developed conditions. The paved areas will be graded so that surface runoff is directed towards a catch basin. Flow will be collected in an underground facility and controlled by a"Flow Control Manhole". The multiple orifice outlet is sized for a staged storage release. An overflow bypass is provided in the event of control structure failure or for storm events that exceed the design criteria. WATER QUALITY CONSIDERATIONS On site paved areas exposed to vehicular traffic is relatively small at less than 5,000 square feet. Wster quality control will be provided by means of dead storage in each of the four on-site storm retentfon system manholes. The depth uf the manholes has been increased to a minimum cf 36" below the invert elevation to allow for the dead storage.