20090083 Ver 1_Emails_20090717 (2)

Chapman, Amy
From: Thibodeau, Peter [[e-mail]]
Sent: Friday, July 17, 2009 10:38 AM
To: Chapman, Amy
Cc: Levitas, Steve; Massengill, Robert; Waldroup, Kenneth; Crisp, Dale; Bachl, Carolyn; Doucette,
Bill
Subject: Neuse River WWTP: Draft response to request for information on treatment wetland design
guidance
Amy-
Thanks for the time to talk on Monday this week to discuss AECOM's response to comments for the proposed subsurface
treatment wetlands at Neuse River Wastewater Treatment Plant. Based on our discussion, I am providing this response
to answer an outstanding question you identified during our conversation. As we discussed, this response (if deemed
complete by DWQ) would allow us to keep things moving forward without need for another Request for Additional
Information, assuming there are no other comments on 6/22/09 our response.
As we discussed, the question you framed was a request for information that describes how AECOM developed the
design for the subsurface treatment wetlands, with identification of the standards, guidance, etc. that were used as the
basis for design.
Response:
The May 1, 2009 application included the report, "Proposed Subsurface Flow (SSF) Constructed Wetlands, Neuse River
Wastewater Treatment Plan, Raleigh, North Carolina" (AECOM, April 2009). This report includes discussion of the design
of the subsurface flow wetlands (see Section 2). As discussed in the report, the conservatively protective wetland designs
were developed in accordance with "Treatment Wetlands" (Kadlec and Knight, 1996) and "Constructed Wetlands for
Wastewater Treatment" (Hammer, 1989). Subsurface treatment wetland design calculations were included in Appendix
B, which documents calculations for treatment wetland size, treatment wetland dimensions, nitrate removal rates, and
hydraulic calculations for the systems that were performed using HydroCAD v. 8.00. Assumptions and estimates used to
develop the sizing calculations and potential effectiveness/nitrate removal efficiency were included in the report. The
references used to guide the design, Kadlec and Knight (1996) and Hammer (1989), are widely accepted as standard
practice for engineering design of constructed treatment wetlands.
Additionally, documentation of the design guidance was also provided in AECOM's June 22, 2009 response to DWQ's
May 21, 2009 comments:
"AECOM used the published text, Treatment Wetlands, by Kadlec and Knight (1996), CRC Press LLC, for design
guidance of this site specific solution to elevated nitrogen concentrations in baseflow discharge". (page 2)
As we have maintained throughout this process and stated in AECOM's June 22, 2009 response, the
proposed subsurface treatment wetlands are not intended to be stormwater wetlands in the manner described in the
NCDENR Stormwater BMP Manual and the design was not based on capturing and treating storm runoff, as there is no
"discharge of stormwater" associated with the "development of land for residential, commercial, industrial, or institutional
use" as stated in 15A NCAC 02H.1001.
We look forward to your review and approval of our application. We have received the US Army Corps of Engineers
Nationwide Permit 18 for this project, and look forward to implementing this environmental solution for addressing
elevated nitrogen concentrations in the identified streams.
Please let me know if this draft response appropriately addresses your question and request for clarification per our
discussion. If you feel that this misses the target of your request, please let me know and we will revise and resubmit for
you.
If needed, we would be happy to provide copies of the referenced guidance documents to you as part of this process
As always, please feel free to contact me with any questions or comments.
: regards,
Peter
Peter M. Thibodeau, Ph.D., P.G., P.H.
Program Manager
AECOM Environment
D 919-872-6600 x231 C 919-280-5882
Peter. thibodeau(o)aecom.com
AECOM
7041 Old Wake Forest Road
Suite 103
Raleigh, NC 27616
T 919-872-6600 F 919-872-7996
C 919-280-5882
www.aecom.com