20130686 Ver 1_Stormwater Approval_20141205

Fox, Tim
From:
Devane, Boyd
Sent:
Thursday, December 04, 20141:50 PM
To:
Fred Grogan
Cc:
Fox, Tim
Subject:
FW: Lake Craig BMP #13 -0686
Attachments:
xs ce112.pdf, planspotadjustments_Ce112.ledf; underdrain detail.jpg
I have looked at the modifications that you have proposed in the approved stormwater plan for the 42 bioretention cell
for the Lake Craig project. I have concluded that the changes as proposed and described in your December 3, 2014
email (attached) are consistent with the Division's BMP Manual and can be allowed. As I discussed with you by phone
today, you might consider not doing the roll compaction to the subgrade of the biocell and instead using scarification. I
can certainly understand your intent to try to facilitate nitrogen removal via the IWS practice as provided in our
Stormwater BMP Manual. However, the option of facilitating infiltration might provide better overall environmental
protection by minimizing and removing mass load in the discharge. Please consider this note as the official DWR
approval of your request for the stormwater plan modification.
From: Fred Grogan r mailto :fredCrneauinoxenvironmental mm]
Sent: Wednesday, December 03, 2014 6:27 PM
To: Devane, Boyd
Cc: Fox, Time mcoates@ashevillenc aov; 'Mike Lewis'; 'Ben Cathey'
Subject: Lake Craig BMP
Boyd -
Per Mike Lewis and McCray Coates conversation with Tim Fox yesterday, I am sending this e-mail to request approval to
adjust bioretention cell 2 at the Lake Craig project.
As a precautionary measure prior to installation, a test pit was excavated +/-2' below the original bioretention cell
bottom elevation in which water was later observed. Although it was not verified that this was indeed the SHWT,
approval of reduction in the cross section of the bioretention cell is being requested as a conservative measure. After
exhaustive exploration of options considering both the as -built infrastructure and existing conditions, it was determined
that this cross section reduction would be the most feasible solution. However, this will result in a few deviations from
the BMP design manual.
1. The bottom of the cell will clear the observed water by approximately 1.5', while if IWS of 0.75' is included, the
clearance would be over 2'.
2. Minimum media depth is suggested at 3' to support trees /shrubs and 2' for grass. We will have 2.25' total
media depth, but have woody material specified. Fortunately, the originally approved under drain detail
(attached) will not prohibit root systems from growing through all zones and into the in -situ soils.
3. Reduction of temporary pending to 6" due to as -built infrastructure constraints.
4. The bottom of the cell is to be roll compacted (as opposed to scarified as suggested) to reduce infiltration rates.
Please see the attached hand sketch & plan of the proposed adjustments for reference.
We have also verified that we still meet volume requirements with the proposed reductions.
Please let us know if these adjustments are acceptable.
PS. This e-mail was initially sent to Tim, but upon clarification of yesterday's conversation, I am forwarding it to you.

Best,
Fred Grogan, RLA
Land Planner
EQUINOX
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37 Haywood Street, Suite 100
Asheville, NC 28801
(828) 253 -6856 extension 203
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