SW5140801_Response To Comments_20220923

TIMMONS GROUP
YOUR VISION ACHIEVED THROUGH OURS.
Project: NCNG Camp Butner Training Center ACFT Fitness Area
Date: 9/23/2020
Contact: Jake Lewis, PE
Phone: [phone]
Email: [e-mail]
Comments from NCDEQ review has been addressed below. Our responses are in red.
Construction Document Submittal First Submittal Comments — 08/30/2022
NCDEQ REVIEW COMMENTS
Jim Farkas (919-707-3646, jim.farkasl'a�x�cdenr.govl
1. This project is located within the Falls watershed and the project is owned by a federal entity.
Please ensure that the requirements outlined in 15A NCAC 02B .0281 are being met.
TG Response: The SNAP tool has been used to calculate nutrients for the site. The site boundary
has been expanded to include adjacent protected forest that the North Carolina National Guard
is using as a safety buffer between 2 roads. The SNAP nutrient calculations have been added to
the narrative and calculations book. Sheet C3.3 has been added to show the updated site
boundary.
2. Please clarify how much BUA will exist on -site in both existing and proposed conditions (so
that the % BUA calculation may be verified since this project is located within a critical WS-
III watershed (per 15A NCAC 02B .0275(2) and is limited to a maximum of 30% BUA). Plan
sheet C3.1 indicates that there is 26,671 sf (:� 0.61 ac) of BUA on -site in existing conditions
(but does not show the location of this BUA (the layer may be turned off?)), but the BUA
summary in the stormwater narrative indicates that there is only 0.06 ac of existing BUA
on -site. Similarly, plan sheet C3.2 indicates that there will be 72,313 sf (:� 1.66 ac) of on -site
BUA draining to the SCMs and there appears to be additional BUA located on -site, but not
draining to the SCMs (Portions of the gravel area& road in the north, northeast, and east
parts of the project area) that would increase the on -site BUA in proposed conditions
above 1.66 ac (the amount shown in the stormwater narrative). Please revise as needed.
You may wish to include a bypass area on the plans/stormwater narrative indicating how
much BUA is located on -site but bypassing the SCM so that the total amount of BUA on -
site in proposed conditions can be determined.
TG Response: The existing impervious is now shown as a hatch on C3.1. Note that upon
investigation of the existing impervious, it is actually only 21,356 sf. With the lower than
expected existing impervious, our design was bypassing too much impervious. The grades
and pond calculations have been modified so that the pond will treat additional
impervious. The bypass impervious has been shown as a hatch on C3.2. The site area
boundary has been modified to better reflect the ACFT area and surrounding forest that
will remain. The % BUA in the post -project condition is 15.5%. The pre and post site
impervious numbers have been updated everywhere. Updated drawings and calculations
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are attached.
3. There appears to be a BUA mismatch between the information shown in Section IV, 10 of
the Application and as shown on the Drainage Area Page of the Supplement-EZ Form. The
BUA in the Application is all shown under the "Other" type while the Supplement-EZ form
breaks it down into "Sidewalk" and "Future" BUA. Please revise as needed.
TG Response: The BUA classifications on the SUPP-EZ and application have been updated to
match. The application has been updated to show the breakdown of impervious. One thing
to note, the "future" impervious has been moved to current and broken out accordingly.
Updated forms are attached.
4. Wet Pond MDC 1, 2, & 3 — Please do not include the sediment storage zone in the main pool
calculations. Plan sheet C5.4 indicates that the excavated bottom of the pond (bottom of
the sediment storage zone) for the main pool is at elevation 478.0' and that the top of the
sediment storage zone is at elevation 479.0'. The sediment storage table in the calculation
booklet indicates that the top of the sediment storage zone is at elevation 478.0'. Please
revise as needed. NOTE: The pond cross-section on plan sheet C5.4 indicates that the top of
the sediment storage zone for the forebay is at elevation 478.0' but the plans (cross-section
on sheet C5.4 and grading on sheet C3.0 seem to indicate that the forebay and main pool
bottoms/sediment storage zones would be at the same elevation. Please revises if needed.
TG Response: Elevation 478.0 is the top of the sediment storage in the forebay and the main
pool. The calculations are correct, but the detail had an error in it. The detail has been
updated to show 478.0 as the top of the sediment storage in the main pool. Updated
drawings and calculations are attached.
Wet Pond MDC 4— Please indicate the location of the forebay weir on the plans. The detail
provided on plan sheet C5.4 indicates that there is a riprap lined weir on the forebay berm,
but the plan views of the pond do not appear to show this. It is recommended to place the
weir as far away from the outlet structure as possible to increase the flow path of the pond
and prevent short-circuiting. Please also increase the elevation of the forebay embankment
so that the pond does not short-circuit since the inlet and outlet are located fairly close to
each other and the top of the forebay embankment is at the permanent pool elevation (it
does not currently impact the flow path of the temporary pool).
TG Response: The forebay weir is now shown on sheet C3.0. The elevation of the forebay
berm was raised by 1-ft to 485 (and updated on the wet pond detail on sheet C5.4).
Updated drawings are attached.
Please correct the following information for the Supplement-EZ Form:
a. Drainage Area Page:
Please complete the entire site column. The entire site column is an
accounting of all of the BUA located within the project area (notjust a sum
of the DA columns). The entire site column should include the on -site BUA
that drains to the SCMs plus the BUA that is located on -site but bypasses
the SCMs.
b. Wet Pond Page
i. Lines 20 & 21— Revise if needed (see earlier comment).
ii. Lines 27 & 28 — Revise if needed (see earlier comment).
iii. Lines 43 & 44 — Per the provided plans, the bottom of the forebay at the
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entrance is shown to be at elevation 477.0', the bottom of the forebay at
the exit is shown to be at elevation 477.5' and the permanent pool surface
elevation is shown to be at elevation 484.0'. This results in a depth to the
forebay entrance of 84" (484.0'-477.0') and a depth to the forebay exit of
78" (484.0'-477.5). Please revise as needed.
TG Response: The total site column has been filled out for the SUPP-EZ. The wet pond detail
had the error in it, not the calculations, so lines 20, 21, 27 and 28 are correct. Lines 43 and
44 are correct. The forebay detail has been updated such that the entrance of the forebay is
elevation 478.00 and the exist of the forebay is 479.00. Updated drawings and calculations
are attached.
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