HomeMy WebLinkAboutWPO201300035 Correspondence 2013-05-13 Michelle Roberge
From: Charlene Harper[charper @Geosyntec.com]
Sent: Wednesday, June 26, 2013 10:04 AM
To: Michelle Roberge
Cc: Chris Cocker; courtney.r.fisher @dom.com
Subject: Hollymead Comments
Attachments: 2013.06.17 Hollymead.pdf; E2_wpo_Hollymead Substation Expansion-Minor Amendment to
SDP-1984-60 .pdf
Follow Up Flag: Follow up
Flag Status: Flagged
Hi there Michelle,
I'm sorry we keep missing each other-I'd love to walk through this by phone so that we can be sure that the next
submittal can be final.
You have a comment,2a, regarding the water quality calculations. We originally used the site area to figure our goals
(6.92 ac), and from the comment it looks like you would prefer us to use the area to the outfall channel to set our
removal goals(1.91 ac). Am I interpreting this correctly? If so, and because the outfall channel is a riprap channel
connection to the pond, I propose that we use the area that directly drains into the pond (including the direct sheet
flow). I've attached a sketch of that scenario for you to see. This would result in a water quality goal setting area of 4.96
acres, l(pre)=20.28%and l(post)=21.53%. Our removal requirement could then be accommodated with the grass swale.
Given the nature of the substation cover,which is primarily uncompacted, angular gravel, I think this solution works very
well and will sufficiently protect the water quality of the pond.
For comment 2b,we tried what you suggested to increase the volume of the pipe storage and remove the 9" orifice;
however,this did not result in the reductions we needed in order to maintain the same flows in the discharge channel.
We would like to keep the design as shown please. Because it is being used as an underground stormwater
management system,the 10-year storm analysis is the pond model--it demonstrates that the system has adequate
capacity to handle the 10-year event within the pipes.
I believe these are the last 2 outstanding issues. I look forward to discussing this with you further at your earliest
convenience. The best number to reach me is 804-393-9350. Thank you!
Charlene
Charlene Harper,P.E.,LEED AP
Senior Engineer
,„„
9211 Arboretum Parkway,Suite 200 Iec t o c
Richmond,VA 23236
Phone: 804-767-2206 ext.2215
cell: 804-393-9350 Cons • , • n s
Fax 804-767-2182
www.geosyntec.com
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