SW3130303_Response to Comments_20130423

WITHERS & R"ENEL
ENGINEERS I PLANNERS i SURVEYORS
LMER OF 7RAM K]MaL
115 MacKenan Drive
Cary, North Carolina 27511
Tel.:[phone] Fax:[phone]
TO: North Carolina Division of Water Quality
Stormwater Permitting Unit
1617 Mail Service Center
Raleigh, NC 27699-1617
WE ARE SENDING YOU
❑ Shop Drawings
❑ Copy of Letter
oATE
04119113
Job No.
02090060
ATTENTION
Robert Patterson
RE:
Kingdom Hall of Jehovah's Witness
® Attached ❑ Under separate cover via the following
❑ Prints ❑ Plans ❑ Samples Specifications
❑ Change order ❑ Diskette ❑
COPIES
DATE
NO.
DESCRIPTION
1
04/18/13
Response to Comments
1
04/18/13
Pond Design Report
1
04/18/13
Copy of Revised O&M for Wetland
1
1 04/18/13
Copy of Revised O&M for Wet Detention Basin .
1
04/18/13
Seasonal High Water Table Evaluation Report
2
04/18/13
Plan Sets
THESE ARE TRANSMITTED as checked below:
® For approval ❑ Approved as submitted ❑ Resubmit copies for approval
❑ For your use ❑ Approved as noted ❑ Submit copies for distribution
❑ As requested ❑ Returned for corrections ❑ Return corrected prints
❑ For review and comment ❑
❑ FOR BIDS DUE 20 ❑ PRINTS RETURNED AFTER LOAN TO US
REMARKS:
COPY TO: SIGNED: Jennifer Diaz
If enclosures are not as noted, kindly notify us at once.

WITH ERB u: RAVEN EL
ENGINEERS I PLANNERS I SURVEYORS
April 18, 2013
Mr. Robert D. Patterson, PE
NCDENR — Stormwater Permitting Unit
1617 Mail Service Center
Raleigh, NC 27699-1617
Re: Kingdom Hall of Jehovah's Witnesses Phase 1 — Stormwater Project No. SW3130303
Dear Mr. Patterson,
Withers & Ravenel has reviewed your comments dated March 28, 2013. Your comments have
been copied below; our responses are italicized:
Please submit the application (SWU-101) and the O&M Agreements with original
signatures. The ones submitted were photocopies.
Response: The Application and O&M Agreements that were submitted previously were the
originals. Withers & Ravenel retained copies for our records but no longer have the originals. The
revised O&M Agreements have been included with this submittal.
2. A SHWT elevation determination must be done within the footprint of each BMP proposed.
No site specific soils information was provided, and this item was left blank on the
supplement forms.
Response: The SHWT elevation determination was prepared by Soil Services PLLC. The report has
been included in this submittal and the supplement forms have been revised.
3. Please delineate and show on the plans the drainage areas to each of the two BMPs;
including the area of the BMP itself.
Response: A drainage area map has been provided with this submittal. It has been included as
part of the stormwater management report in the Site Information section.
4. Please show all wetlands and surface waters on the plans, or if there are none, provide a
note to that affect.
Response: There are no wetlands or surface waters on site. A note to that effect has been added to
the Site Plan (Sheet 2.0).
115 MacKenan Drive I Cary, NC 275111 tel.: [phone] fax: [phone] www.withersravenel.com 1 License No. C-0832
1410 Commonwealth Drive 1 suite 1oi 1 Wilmington, NC 28403 1 tel: [phone] fax: [phone]
7011 Albert Pick Road, Suite G 1 Greensboro, NC 27409 1 tel: 316.6o-,.3ooq 1 fax: [phone]B

WITHERS &-RAVENEL
5. Page 3 of the Wet Pond O&M Agreement: The bottom and sediment cleanout elevations
are not consistent with the plans, talcs, and supplement forms.
Response: Revised per comment.
6. Wet Pond:
a. On sht. 6.0:
i. It is not clear if the "void space" on the riser detail is a weir or not?
Response: The 'void space" on the riser detail is the space between the riser crest and the top
slab, not an additional weir. The detail has been revised to provide more clarity.
ii. The cross section needs to show the 10:1 vegetated shelf.
Response: Revised per comment.
b. The orifice size is not shown consistently on the plans, talcs, and supplement forms
(1"and 2" is used in different places).
Response: The orifice size and elevation were adjusted as a result of the SHWT findings. The
orifice size was adjusted to 1.5". Al! references to the orifice size and elevation have been revised.
c. Based on the 2" orifice shown on the plans, the minimum required treatment
volume (5928 cf) will drawdown in less than the minimum required 2 days.
Response: The drawdown was recalculated with a 1.5" orifice and the time is now 2.29 days.
d. Based on the surface areas provided, the average depth appears to be less than the
3' minimum required.
Response: The average depth was calculated using "Option 2". The calculations have been
provided in the stormwater management report.
e. Please provide a hardened emergency spillway. None was provided.
Response: The proposed riserlbarrel outlet is a combination spillway, the primary spillway being
the drawdown orifice, the emergency spillway being the riser crest. An additional routing showing
a worst case scenario with the primary being clogged and the routing beginning at the riser crest
has been. provided as the basis for this design without an additional spillway. This ensures the
pond will not overtop in a 100-year storm event even with the orifice blocked.
f. The outlet structure input for the routing calculations is not consistent with the
plans.
Response: Revised per comment.
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WITHERS &"FZAVENEL
7. Constructed Wetland:
g. On Sht. 6.1: A minimum of 4 of topsoil needs to be shown on the cross section.
Response: Revised per comment.
h. Dependant on the SHWT and site soils, the deep pools may need to be lined or
compacted to maintain the water level.
Response: The SHWT results indicate that a liner is not necessary since the proposed normal pool
is within +6" of the SHWT.
i. Please consider providing a more stable and adjustable outlet control structure.
Response: Other outlet structures were considered, however the proposed outlet structure was the
best option considering site constraints.
8. Please note that the volume used in the drawdown calculations for both BMPs should be
based on the minimum required treatment volume (for the 1 "), not the whole temporary
pool volume provided.
Response: Revised per comment.
9. Please be sure to revise all forms, plans, and calculations to reflect any changes.
Response: Revised per comment.
The revised plans and stormwater management report have been provided with this submittal. The
revised O&M forms have been provided as well. We hope to have addressed your concerns. If
you should have any further questions or comments please do not hesitate to contact us.
Sincerely,
WITHE (- RAVENEL
)ennife
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