HomeMy WebLinkAbout20023-06-07 Filtera Bioscape Sizing Memo
June 8, 2023
Tom Chiado
(206) 550-8363
tom@chiadollc.com
RE Bioscape Size Reduction Due to Turf Infill Revision
Dear Tom:
With the recent decision to change the infill of the two turf fields on the Seattle Sounders Headquarters project
we want to take the opportunity to review the requirements for water quality sizing that was identified in final
decision from the Hearing Examiner for the City of Renton.
The decision at that time was the Filterra Bioscape should be upsized from the standard 91% with applicable K
factor, per the 2022 City of Renton Surface Water Design Manual, to the 2-year storm event due to the SBR
Crumb Rubber infill and the concerns related to 6PPD-Q.
Due to these changes, we propose revising the Filterra Bioscape sizing to align with the 2002 City of Renton
Surface Water Design Manual standards. The Filterra Bioscape area will reduce from 825 sf to 638 sf.
Attached are revised calculations for the bioscape sizing, as well as a comparison drawing showing the
reduced size.
Sincerely,
COUGHLIN PORTER LUNDEEN, INC.
William Andres, P.E.
Civil Project Manager
Treatment Flow Rate*
91st % Storm WQ Q 1.3192 cfs (Determined from WWHM)
k Factor 1.91
Treatment Flow Rate 2.52 cfs (City of Renton/KC factor)
Bioscape Media Filtration Rate
175 in/hr
14.58 ft/hr
0.0041 ft/sec
100 in/hr
8.33 ft/hr
0.0023 ft/sec
Bioscape Area Required
(Enhanced Basic)622.0 sf 0.0143
(Phosphorus)1088.5 sf 0.0250
Area Provided 638 sf 0.0146
Sounders - Longacres
Phosphorus
Enhanced Basic
Stormwater - Water Quality Calculations
3Bioscape Enlargement
15
15
20
16
16
16
17
18
19
21
15
15
20
16
16
16
17
18
21
73.2'
76'
R5'
R5'TE O F WASH
I
NGC
ORB.BYHTOM WKCurrent Approved Design
Proposed Reduction for Cork Infill
825 SF
638 SF