SW4200501_2020-05-08 Comment Responses_5/26/2020

CLH design, p.a.
400 Regency Forest Drive, Suite 120
Cary, North Carolina 27518
P: 919.319.6716 C L H
www.clhdesignpa.com aEsiC__N
Site Plan Comment Responses
Date: May 15, 2020
Re: Lewisville Middle School- Forsyth County - State Project SW4191201
Dear Jim Farkas :
Below in red are our responses to the 4t" round of review comments received for the above referenced project.
Division of Energy, Mineral and Land Resources
Comment 1: Original Comment 5 — No note was found on any of the provided plan sheets indicating the
presence or absence of existing, on -site wetlands. Section VI, 8m requires that either a wetland
delineation or a note stating no wetlands are present, in addition to the name and title of the
individual that provided this determination, be included within the plan set.
Response: Note has been added in the notes section of most plan sheets. See sheet CO3.01-0O3.04 for note
stating there are not wetlands present on this site. This statement includes the firm and the
person who performed the delineation and report.
Comment 2: Original Comment 7 — The provided stage -storage table for the stormwater wetland indicates
that the wetland will hold approximately 3,800 cf of water at elevation 813. The design volume
for this facility is 2,822 cf. The temporary ponding elevation should be based off of the actual
elevation that the design volume will fill the wetland up to (stormwater Wetland MDC 1). Since
most all of the sizing criteria for a stormwater wetland are based on the temporary ponding
depth (stormwater Wetland MDC 3), it is important that this be accurately calculated.
Response: Wetland sizing spreadsheet has been revised to show the drawdown time calculated using the
design volume and the depth of where the design volume occurs. The recalculated drawdown
time is still within the 2-5 day period (MDC 10). See revised calculations booklet. The zone
allocations have been revised to reference the surface area at the design volume to generate the
percentages of each zone. Please see wetland sheet of supplement-EZ form as much of these
elevations and numbers have been revised as a reflection of this change.
Comment 3: Original Comment 10, Wet Pond Sheet, Line 44 — Line 34 indicates that the forebay cleanout
depth (distance from the permanent pool elevation to the top of the sediment storage elevation)
is 54 inches (This also coincides with the forebay stage -storage table's starting at elevation 822).
Line 44 (the distance from the permanent pool elevation to the excavated bottom of the forebay
near the exit) must be at least 6 inches greater than Line 34 (to be compliant with Wet Pond MDC
3) and Line 43 (the distance from the permanent pool elevation to the excavated bottom of the
forebay near the entrance) must be greater than Line 44 (to comply with Wet Pond MDC 5b).
Since the contours are not precise enough to show these half foot elevation differences, please
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Site Plan Comments
May 15, 2020
either clarify the note, provide spot elevations, or clearly show these elevations on the cross-
section to ensure it gets constructed correctly. For example, the plans show that the deepest point
of the forebay is the forebay bottom, at elevation 821.5. The note says that the exit should be 6
inches shallower than the entrance. Assuming that the entrance is the deepest part of the
forebay, the exit elevation would be 822 (821.5 + 0.5) which is the some elevation as the forebay
sediment storage top (Thus violating Wet Pond MDC 3). Clarification is needed.
Response: Line 34 remains 54" which coincides with the state -storage tables provided previously. Line 44
has been revised to be 6" greater than line 34 and is now 60". A spot of 821.50 has been added to
the forebay on the grading sheet CO3.03. Line 43 has been revised to be 6" greater than line 44
and is now 66" at the entrance. A spot of 821.00 has been added to the forebay on the grading
sheet CO3.03. Additional information has been added to the cross section of the wet pond detail.
See sheet C07.04 for additional language.
Comment 4: Original Comment 10, Stormwater Wetland Sheet, Line 28 — The provided note presents the
some issues as noted above. The bottom elevations for the forebay and deep pools (Lines 27-29)
do not correspond with the information shown on sheet C07.05. Please either clarify the note,
provide spot elevations, or clearly show these elevations on the cross-section to ensure it gets
constructed correctly.
Response: The confusion for this comment lies in the fact that the supplement-EZ form should include the
sediment storage depth. Line 27 has been revised to be 6" deeper than the forebay exit plus an
additional 6" for sediment storage. Line 28 has been revised to have an additional 6" lower for
sediment storage. Line 29 has been revised to include an additional 6" for sediment storage.
Detail sheet C07.05 has been revised to have more detail in the section view indicating the
bottom at entrance and exit elevations plus elevations of sediment storage. Spots have been
added to the wetland forebay on the grading sheets as well. Item U in the wetland schedule has
been revised to be clearer to include pond bottom and excavated pond bottom.
Comment 5: Prior Comment 6, Supplement-EZ, Stormwater Wetland, Line 52 — This value should be the
actual number of plants provided in the shallow water zone per 200 sf of shallow water zone (not
just the minimum amount per the MDC). The issue with the form has been noted.
Response: The total number of plants provided in the shallow water zone has been revised to 423 Plants.
This equates to 50 plants per 200 SF.
Comment 6: Prior Comment 7— The plant quantities on sheet C07.06 still do not add up properly. For example,
the shallow water plant list specifies five different types of plants, four of which are shown to
have a quantity of 126 and the remaining one is shown to have a quantity of 127. Adding these
quantities up (126 + 126 + 126 + 126 + 127) results in 631 total plants. The plan sheet indicates
that there are 554 total plants provided for this zone (The some is true for the shallow land plant
list, but the error is not as large, there is only a discrepancy of 1 plant).
Response: The plant calculations have been revised to show the correct number of plants as indicated in
your comment.
The following issues were also noted during review:
Comment 7: Supplement-EZ Form
o Wet Pond Page
■ Lines 22, 24, 46 and/or 47 — Either the slope (10:1) or the height & width (1 ft & 6 ft) of
the vegetated slope is incorrect. Please either correct the slope (Line 47), bottom of shelf
elevation (Line 22), top of shelf elevation (Line 24), and/or shelf width (Line 46) so that
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Site Plan Comments
May 15, 2020
all of this information is consistent. Please apply these changes throughout the entire
submission.
• Response: Line 47 is revised and should read as 6:1. The elevations and widths
were verified and are consistent with each other.
Line 25 — The elevation of the temporary pool should be based on the design volume
(29,521 cf). Based on the provided stage -storage table, this volume would be stored
below elevation 827.5. Please ensure that this value and the drawdown equation is
recalculated for the temporary pool volum%levation associated with the design
volume. Please apply these changes throughout the entire submission as needed.
• Response: Please refer to the revised wet pond calculations which interpolates
the elevation at the 1" design volume and uses the depth of design volume and
the design volume to calculate the drawdown time. The elevation of the
temporary pool as it pertains to the design volume has been revised based on
the revised calcs. See line 25 in revised supplement-EZ.
Line 37— The orifice diameter, as shown in the calculations and in the plans (2.5 in) does
not match the reported value (3 in). Please revise for consistency.
• Response: This is the excel sheet. It is formatted to round up. I have hard typed
in the supplement-EZ form ('2.5) which fixes the issue.
Stormwater Wetland Page
■ Lines 23 & 39 — These items contradict each other.
Response: Line 23 has been revised to show the 25-year storm elevation as this
was what was required for the Town of Lewisville. This elevation is 814.13'. The
temporary pool was revised to 812.71, so 814.13-812.71 = 1.42' or 17.04". This
item was hard typed in as the excel spreadsheet is formatted to round up to the
nearest inch.
■ Lines 27-29 — These values do not correspond with the information shown on sheet
C07.05.
• Response: See comment response to comment #4 (this review) also known as
"original comment #10.
Lines 24, 30, 35-40, & 48 — See earlier comment about the stormwater wetland
temporary ponding elevation.
• Response: Line 24 — Temporary pool elevation has been revised based on the
findings in our revised wetland sizing calculation. Lines 35-40 have also been
revised as a result of our calculation revisions. Line 48 has been revised per
previous comment to recalculate drawdown based on the depth of the design
volume. The revised drawdown time is with the 2-5 range and abides by the
wetland MDCs.
Line 42 — The distance from the permanent pool elevation to the forebay entrance (30 in)
does not match the difference between Line 25 (812) and Line 27 (810) (812 — 810 = 24
in).
• Response: See previous comment #4 as the elevations have been revised. 812 —
809 = 3' or 36".
Line 43 — The distance from the permanent pool elevation to the forebay exit (24 in) does
not match the difference between Line 25 (812) and Line 28 (810.5) (812 — 810.5 = 18 in).
NOTE: 18 in is less than the requisite 24 in (Per Stormwater Wetland MDC 6).
• Response: See previous comment #4 as the elevations have been revised. 812 —
809.5 = 2.5' or 30".
CLH design, p.a.

Site Plan Comments
May 15, 2020
It is recommended that:
Comment 8: Deep pool plantings not be planted in the deep pool nearest the outlet as they may cause
clogging.
Response: This wetland is very small, and we only have the one deep pool area. In order to meet the state
requirements, we must plant in this area. We have added a note that no plants are to be planted
within 3' of the outlet structure to help with this concern.
Comment 9: FYI, since having issued my previous round of comments, I received clarification from within the
Department that all SCMs with off -site drainage need to have either the legal agreement in place
between the property owners limiting the amount of off -site BUA that will drain to the facility or
be designed in accordance with 15A NCAC 02H .1003(3)(b). The Department's preferred option is
to have the legal agreement in place as it is the best method for ensuring long-term compliance
with the permit, but 15A NCAC 02H .1003(3)(b) is also acceptable since it is statute. Diverting the
off -site drainage around an SCM is still an option.
Response: In lieu of acquiring a legal agreement, we have considered the offsite portion of the site to be
100% impervious and is being treated by the wet pond. This allows for no restrictions on the
offsite portions for future development. A note has been added to the drainage area sheet of the
supplement-EZ form and noted in the narrative stating this. On the drainage area sheet for the
Wetpond (drainage area 1) lines 5, 7, 10 'future" have all been revised to reflect this change.
End of Responses
Thank you for all your help and please call with any questions.
Sincerely,
For CLH design, p.a.
Renee Pfeifer, PLA
Vice President
CLH design, p.a.