7220 RAINIER DR 2018-01-01 MF Import

INTRODUCTION This report will analyze the existing and proposed drainage for the development of two parcels located in the NW 'i of Section 7, Township 28 North, and Range 5 Eas;, W.M. all within the City of EverEtt limits. The site is bounded by unopened right-of- way for 74�h Street SE on the northside and by unopened right-of-way for Rainier Dr. on the eastside. The site is approximately 0.51 acres. EXISTING CONDITIONS Existinq Site Description The site is currently an asphalt parking lot serving as overFlow parking for the adjacent businesses to the east. Most of the site is paved with gravel on the outer perimeter of the parking area. The parking area is bounded by a ditch on the north and east side. The stre ambanks of the ditch is vegetated with grass, brushes, and a few trees (see Photo 1;. Soils The soil has beer� identified as Aiderrvood-Urban land complex, 2 to 8 percent slopes. This soil is moderately deep, drains well, and was formed in glacial till. Runoff is siow and depth to the hardpan ranges from 20 to 40 inches. Permeability is moderately rapid above the hardpan and slow through it. The hydrologic group type is C for this soil. Also included in this unit are small areas of McKenna soils with a hydrologic group D. Existinq Drainaqe Most of the runoff sheet flows to the east and northeast into the east and south ditch adjacent to the site. The south ditch begins at the southwest corner of the site and flows easterly. At the southeast corner the south ditch turns north and becomes the east ditch flowing northerly (see Photo 2). Runoff in the east ditch outfalls into a 36- inch concrete pipe (see Photo 4) and enters a catchbasin and pipe system flowing northerl,. Both ditches are located within the unopened right-of-way for 74`h Street SE and Rainier Drive. There are several storm sewer pipes outfalling along the ditch channel; one 12-inch concrete, one 30-inch HDPE (see Photo 3). Most of the runoff from the adjacent apartments, townhomes, houses, and street discharge into this ditch. UPSTREAM ANALYSIS Runoff from approximately 13.61 acres south of the site drains into the ditch (see Basin Map in the Appendix). This area is highly urbanized and stormwater from this area contribute to the headwater of Pigeon Creek No. 1. Capacity analysis for the existing ditch, proposed 36-inch concrete culvert, and existing 36-inch concrete outfall pipe can be found in the appendix. Tubbs & Duesenberg Apartments Page 2 Drainage Report