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Page 1 of 2 <br />Kirk Brooks. <br />From: Jane Zimmerman <br />Sent: Monday, January 07, 2008 2:15 PM <br />To: 'Schwin Chaosilapakul' <br />Cc: Kirk Brooks <br />Subject: RE: LDS Parking Lot Comments <br />Hi Schwin - <br />I'm often away from my desk, but I try to return messages as promptly as I can. Please leave <br />a message next time. <br />You don't actually need to provide detention for the off -site flows, but you do need to account <br />for the flows that will run onto the pavement from the adjacent areas. Treat these as part of <br />your existing flow calculations for the 2yr, 10 yr, and 100 yr storms. You shouldn't end up <br />providing any additional detention, but the orifice sizes will reflect the actuality of the additional <br />flow. <br />With regard to treatment - stormwater treatment systems must be sized for the flows that <br />actually enter into and pass through them. System efficiencies are based on flow rate and or <br />volume. If you size the system only for the runoff from your site, yet there is a significant <br />amount of additional flow entering the system, as there is in this case, the small system would <br />be overwhelmed and would not efficiently treat much of anything! <br />You have the alternative of collecting the off -site flow into a separate system, bypassing it <br />around your site's treatment and detention features, and discharging it to the last cb on the <br />site. Then you would not have to account for the off -site flow in either the detention or <br />treatment calculations. <br />Jane <br />Jane Zimmerman, Sr. Engineer <br />City of Everett Public Works Department <br />phone: 425-257-8885 fax: 425-257-8882 <br />e-mail: /zimmerman@ci.everett.wa.us <br />From: Schwin Chaosilapakul [mailto:Schwin@patrickharron.com] <br />Sent: Monday, January 07, 2008 1:32 PM <br />To: lane Zimmerman <br />Subject: LDS Parking Lot Comments <br />Hi Jane, <br />Missed your call this morning and i can't seem to get a hold of you at your desk. Anyway, I've gone through your <br />comments and have a question - Why are we required to provide detention and water quality for the offsite <br />stormwater? Give me a call to discuss when you get a chance. Thanks. <br />Schwin Chaosilapakul, P.E. <br />Patrick Harron & Associates, LLC <br />�2 <br />1 /7/2008 <br />