SW4200501_2020-07-01 Comment Responses_20200702

CLH design, p.a.

CLH design, p.a.CLH design, p.a.CLH design, p.a.CLH design, p.a.
400 Regency Forest Drive, Suite 120
Cary, North Carolina 27518
P: 919.319.6716
www.clhdesignpa.com

Site Plan Comment Responses
Date: July 1, 2020
Re: Lewisville Middle School- Forsyth County - State Project SW4200501

Dear Jim Farkas :

Below in red are our responses to the 6th round of review comments received for the above referenced project.

Division of Energy, Mineral and Land Resources
Comment 1: There appears to be a discrepancy in the drawdown orifice size for the proposed stormwater
wetland. The plans and Supplement-EZ Form indicate that the diameter of this orifice is 0.75 inches whereas the
drawdown calculations show 1.00 inch. Please revise as needed for consistency.

.
Response: Drawdown calculation has been revised to 0.75 as to be consistent with the hydrograph routings
and supplement-EZ forms. The drawdown time adjusted and this was revised on the supplement-
EZ form.

Comment 2: Supplement-EZ Form:
o Wet Pond Page:
 Line 27 – The volume of the main pool is shown as 87,015 cf in the Supplement-EZ Form
and as 86,817 cf in the calculations. Please revise as needed for consistency. If this is
due to different volume calculation methodologies, just explain that in the response to
these comments and explain how the volumes on the calculation sheets are calculated.
Response: If you refer to the wet pond sizing calculations you will see the breakdown of
how this calculation breaks down the main pool volume. This discrepancy is a result is
different calculation methodologies between the spreadsheet and our hydrograph-pond
routing model. The discrepancy is small and not enough for concern. No changes have
been made to the calculations or supplement-EZ due to this comment.
 Line 32 – The volume of the forebay is shown as 14,313 cf in the Supplement-EZ Form
and as 13,845 cf in the calculations. Please revise as needed for consistency. If this is
due to different volume calculation methodologies, just explain that in the response to
these comments and explain how the volumes on the calculation sheets are calculated.
Response: If you refer to the wet pond sizing calculations you will see the breakdown of
how this calculation breaks down the forebay volume. This discrepancy is a result is
different calculation methodologies between the spreadsheet and our hydrograph-pond
routing model. The discrepancy is small and not enough for concern. Using the values
presented in the pond routing, the volumes still fall within the appropriate range. No
changes have been made to the calculations or supplement-EZ due to this comment.

Site Plan Comments
July 1, 2020
CLH design, p.a.

o Stormwater Wetland Page:
 Line 29 – The bottom elevation of the non-forebay deep pools is shown as 809.5 ft in
the Supplement-EZ Form and as 810 ft in the plans. Please revise as needed for
consistency. If this is due to different volume calculation methodologies, just explain
that in the response to these comments and explain how the volumes on the calculation
sheets are calculated.
Response: Supplement-EZ form has been adjusted to be consistent with what is on the
plans-810.00’.

Comment 3: O&M Agreement Form, Wet Detention Pond Design Summary:
o Forebay:
 The sediment removal elevation is shown as 821 ft but the plans indicate 822 ft.
o Main Pond:
 The sediment removal elevation is shown as 822.5 ft but the plans indicate 823 ft.
 The bottom elevation is shown as 823 ft but the plans indicate 822.5 ft.

Response: O&M revisions have been adjusted per the comments above.

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