NCG060387_Email RE Stormwater Retaining Wall Secondary Containment_20180801

Georgoulias, Bethany
From: Georgoulias, Bethany
Sent: Wednesday, August 01, 2018 11:20 AM
To: 'Patrick Hirl'
Cc: Bennett, Bradley; [e-mail];
[e-mail]; Lucas, Annette
Subject: RE: [External] Stormwater Retaining Wall
Patrick,
This is an acceptable approach to provide improved secondary containment at this time. Please ensure that the valve
can be secured closed with a locking mechanism, as specified in the permit.
I understand from correspondence with Chad Broadway that the volume of the largest tank is about 2.2 million
gallons. We recognize that retrofitting this site to provide secondary containment that captures that volume, plus
freeboard to allow for the 25 -year, 24-hour storm (as defined in Part IV) would require a significant site re -design effort
and much longer time line. We agree that the proposed retention measures and the ability to prevent any contaminant
release with a locked valve will provide a significantly better and more stable measure of spill release prevention at this
site.
Should additional spill releases, housekeeping concerns, or potential impacts to water quality arise; or should other
compliance issues arise, the facility may be required to install more containment measures or implement specific best
management practices.
Best regards,
Bethany Georgoulias
Environmental Engineer
Stormwater Program, Division of Energy, Mineral, and Land Resources
N.C. Department of Environmental Quality
919 707 3641 office
bethanygeor oulias e ncdenr.gov
512 N. Salisbury Street, Raleigh, NC 27604 (location)
1612 Mail Service Center, Raleigh, NC 27699-1612 (mailing)
Website: httD:Hdea.nc.aov/about/divisions/enerLv-mineral-land-resources/stormwater
Email correspondence to and from this address is subject to the North Carolina Public Records
Law and may be disclosed to third parties.
From: Patrick Hirl [mailto:[e-mail]]
Sent: Tuesday, July 31, 2018 10:10 PM
To: Georgoulias, Bethany<[e-mail]>; Bennett, Bradley <bradley. ben [e-mail]>;
[e-mail]
Cc: [e-mail]
Subject: [External] Stormwater Retaining Wall

Bethany,
I wanted to follow-up from our call this morning. As we discussed, we are preparing to install a retention wall at Orbit
Energy anaerobic digestion facility on Johnson Road, Charlotte, NC. The retention wall will capture digester contents
should they be released from any of the three anaerobic digesters. The wall will ensure that they enter the stromwater
collection system and flow to the stromwater retention basin. This basin has a storage volume of 140,000 gallons. As we
discussed, we will install a valve at the bottom outlet of the stormwater retention basin control structure. This valve will
normally be closed to allow for "hold, test, and release" of captured stormwater. We also discussed that the retention
wall would also allow for the covering of the stromwater drains with mats allowing for the storage of an additional
140,000 gallons in the process area.
We will proceed with construction of the retention wall and include the wall and the additional valve on the stormwater
basin control structure in our draft SWPPP.
Regards,
PJH
Patrick Hirl, PE, PhD
Director of Engineering — Biogas
Environmental Resilience and Sustainability
One Park Plaza, Suite 1000
Irvine, CA 92614
M: 612.600.2881
[e-mail]
www.montrose-env.com
APlease consider the environment before printing
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