1001 N BROADWAY EVCC PARKING 2018-12-03

, —I �rould suggest looking at the Ecolo•manual for their recommendations—I belT�e that you will have addressed all my concerns. Thank you again. At this point, I'll be out of the office until 9/10, so I wanted to give you some quick feedback before I depart for"home labor" projects! Jane Jane Zimmerman, Sr. Engineer City of Everett Public Works Department phone: 425-257-8885 fax: 425-257-8882 e-mail.�jzimmerman(a�everettwa.qov From: Leif Johansen [mailto:ljohansen@reidmiddleton.com] Sent: Thursday, September 03, 2015 11:57 AM To: Jane Zimmerman C�: Ding Ye Subject: FW: 1001 N Broadway, building demo and parking lot construction Jane Thank you for proving comments on the parking lot drainage. Our understanding is that you would like to see more parking lot areas drain to the bioretention cells and curbs around the bioretention cells for driving safety. We have modified the parking lot grading to increase the surface area draining to each of the bioretention areas. It was possible to increase the areas drainage to bioretention areas 1 and 2 (see attached exhibit) but due to the steep cross slope of the existing parking lot we were not able to increase the area draining to bioretention area 3. The modification results are as follow: 1. Bottom area of bioretention area 1 is now approximately 8% (comparing to 30%prior to moditication) of the size of the contributing drainage area. 2. Bottom area of bioretention area 2 is now approximately 13% (comparing to 30% prior to modification) of the size of the contributing drainage area. 3. Bottom area of bioretention area 3 is now approximately 21% (comparing to 21% prior to modification) of the size of the contributing drainage area. We recognize that these bioretention areas are large as coinpared to DOE minimum of 5% of the contributing drainage are. And we have tried hard to achieve this 5% goal. However, the existing site condition and the project as a parking lot do not allow us to go that far: 1. The amount of contributing drainage area for each bioretention area is limited due to site grading constraints. The parking lot must tie into existing pavement/curb elevations along all outer edges. We have graded high and low points into the site to pushed runoff into collection points but we have limited flexibility as we try to keep grades at reasonable magnitudes for parking lot use. 2. We would like to keep the bioretention areas larger to encourage water inf ltration. The conservative sizing of thcse bioretcntion arcas will help to encourage infilh-ati�m of a breater portion of site runoff and reduce stormwater entering the drainage systein through the underdrain pipes. This will help to reduce peak flows in the downstream combined sewer system. 2/' ,�