SW3230302_Response To Comments_20230627

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ENGINEERING
NCDEQ
Jim Farkas
State Stormwater Engineer
512 N. Salisbury Street, Office 640M
Raleigh, NC 27604
RE: Davis Village - PROJECT NUMBER #SW3230302
Dear Mr. Farkas:
Thank you for reviewing the Davis Village—single family home stormwater project in Wingate, NC. We are
submitting the revised Davis Village plans, Forms, and Calculations in response to the recent comments we
received in the review, dated May 30, 2023. Below is a list of what is included in this re-submittal as well as a
comment response.
• Civil construction plans (2 copies)
• Stormwater Management Calculation Book (1 copy)
• Comment response letter (attached)
• Revised NCDEQ EZ Form
Please contact Bryan Linton, at Plott Hound Engineering, if you have any questions or need anything further.
Thank you,
--1- _,..-- „.„,, ,,, ,.._ L____
Bryan Linton, PE
[e-mail]
146 Valley Glen Dr.
Waxhaw, NC 28173
[phone]

Comment Response Letter:
1. As designed, the project does not appear to capture and treat sufficient BUA in order for
the project to meet Runoff Treatment (15A NCAC 02H .1002(43)). Please ensure that the
net increase in BUA is being captured and treated in one or more primary SCMs. If it is
not practicable to capture and treat all of the new Bua, the uncaptured areas of the project
can be permitted as a low-density area (provided that they meet all of the low-density
requirements outlined in 15A NCAC 02H .1003(2)). Please also clarify if the provided
deed restriction document (3,500 sf per lot) applies to all of the proposed lots (Lots 1-46
south of Phifer Road and lots 1-186 north of Phifer Road). Per the Supplement-EZ Form,
the total amount of BUA allocated to the subdivided lots for the entire site (Entire Site
Column, Line 9) is 380,640 sf whereas the total amount of BUA allocated to the
subdivided lots per the deed restriction document would be 812,000 sf(3,500 sf/lot * 232
lots). Please revise as needed.
Response: the BUAs has been updated in the spreadsheets and calculations. The SCMs were over-sized to
treat any BUA that bypasses the BMP in all areas of the site. The SCMs treat approximately 88%of all BUA
on the project site. See drainage area map for bypass areas shaded. Hydrographs were updated to include
the over-sized volume and bypass BUA as well.
2. Please provide riprap sizing/design calculations showing that the inlets and outlets are
sized in accordance with General MDC 4.
Response: Riprap Aprons have been sized, labeled in plans (see sheets C417-C419) and calcs included in
report.
3. Please correct the following issues with the Wet Pond Design:
a. The provided calculations show the drainage area to the wet pond as being 30 acres
and containing 50% BUA whereas the other submittal items (Application &
Supplement-EZ Form) indicate that the drainage area to the SCM as being 25.5 ac
and containing 38% BUA. Please revise as needed.
Response: Drainage areas and BUA have been revised to be accurate and consistent.
b. Please provide a cross-sectional view of the wet pond that clearly shows important
slopes and elevations (such as the excavated bottom of the main pool, the excavated
entrance and exit elevations of the forebay, the top of the sediment storage zone, the
cross-slope(s) of the pond, etc...). This item is required per 15A NCAC
02H .1042(2)(h).
Response: Cross section of wet pond included on sheet C417

c. As designed, the forebay appears to be too large (Wet Pond MDC 5). The volume of
the forebay (volume stored in the forebay above the top of the sediment storage zone
and below the permanent pool surface) must be between 25%-20% of the main pool
volume (volume stored in the main pool above the top of the sediment storage zone
and below the permanent pool surface). NOTE: The main pool does not include the
forebay. The forebay is provided in addition to the main pool and, when combined,
the forebay and main pool form the permanent pool. Please revise as needed.
Response: this is correct. The forebay was too large (approx. 35%). The forebay has been re-sized and
revised in the plan sheets on the grading plans, wet pond detail sheet, and wet pond planting plans.
Calculations have been updated and the stage-storage tables revised in calcs and included on sheet C417.
d. Per the provided stage-storage tables, it is unclear what the volume provided in the
main pool or forebay is at elevation 555.5' (since cross-sectional areas are only
provided for whole numbered elevations). Please include the cross-sectional areas
(and volumes) for the forebay and main pool at the permanent pool surface elevation
in the stage-storage table.
Response: tables updated in calcs and included on C417.
e. Please use the latest SA/DA tables (provided in Part C-3 of the Manual) in your
calculations.
Response: SA/DA table updated per available table online in C3.
f. The drawdown orifice (invert at the permanent pool surface elevation) is shown to
have a diameter of 4.0" in the calculations and a diameter of 3.0" in the plans. Please
revise as needed.
Response: 4 inches is correct. Plans and calcs update.
4. Please correct the following issues with the Sand Filters:
a. There appears to be an issue with the drainage area information as shown in the
calculations and as shown in the other submittal items. For example, the calculations
show the drainage area to SCM 2 as 50% BUA whereas the other submittal items
show 34% BUA. Please revise as needed.
Response: Drainage areas and BUAs updated/fixed so they are accurate and consistent.

b. Please provide the SHWT elevations and the lowest excavated bottom elevations for
both sand filters so that Sand Filter MDC 1 can be verified.
Response: Newtech is adding the SHWT for the sand filter south of the Townhomes area. We will send this
updated SHWT report as soon as we receive it.
c. Please ensure that the storage volume provided in each chamber of the sand filter is
equivalent (Sand Filter MDC 2). NOTE: The sediment chamber of the sand filter may be oversized for
detention. If doing so, please ensure that at least half of the minimum required treatment volume can be
stored in each chamber. For example, if the minimum required treatment volume for the SCM is 1,000 cf, the
sand chamber must be able to hold at least 500 cf and the sediment chamber must be sized to hold at
least 500 cf.
Response: stage storage tables added to the sand filter detail sheets (C418 and C419).
d. Please provide stage-storage tables for the sediment and sand chambers so that Sand
Filter MDCs 2 & 3 can be verified.
Response: stage storage tables added to the sand filter detail sheets (C418 and C419).
e. While not required, it is strongly recommended to limit the amount of pervious areas
draining to the sand filter as pervious areas produce fines that can cause the sand filter
to clog and will necessitate more frequent maintenance.
Response: pervious areas are limited as much as possible. The amenity area to SCM 2 and the parking lots
and town homes to SCM 3 help increase impervious areas.
5. Please correct the following issues with the Supplement-EZ Form:
a. Cover Page:
i. Line 7— Per 15A NCAC 02H .1017(10), the minimum required vegetated setback
distance is 30 ft (20 ft provided).
Response: we updated the plans for this earlier this year but the EZ form was submitted before the plans
were updated. The EZ form has been revised to be correct at 30'.
b. Drainage Areas Page:
i. Entire Site Column —The entire site column should be an accounting of the entire
project area (similar to how the drainage area columns ar an accounting of the
entire drainage area to the SCMs), not just a summation of the other columns.
BUA that is located on-site but bypasses the SCMs should be accounted for in this
column. When asked for the "drainage area" of the entire site, please enter the
project area. Please also refer to the earlier comment with regard to the BUA
allocated to the individual lots (Line 9 for the entire site column should correspond
to the total BUA allocated to the lots per the deed restriction document). Lines 4 &
19-21 are not needed for this column.

ii. Line 20— Please see later comments with regard to the design volume of the
SCMs.
Response: The drainage area page on the EZ form was updated and corrected so it matches the site plans
and calculations.
c. Wet Pond Page:
i. Line 2— Please revise this item in accordance with the earlier comment. The
minimum required treatment volume should be based on the actual drainage area
to the SCM. Please revise as needed.
ii. Line 25—The temporary pool elevation is determined by the invert of the lowest
bypass orifice/weir (in this case, the weir at elevation 557.0').
iii. Line 26— Do not include the surface area of the forebay in this item, only the
surface area of the main pool. NOTE: A discrepancy between the provided value
(36,111 sf) and the value used in the drawdown calculations (35,940 sf) was noted,
please ensure that the information in the submission is correct and consistent.
iv. Line 27— Do not include the forebay volume in this item.
v. Line 28— Please recalculate this value. NOTE: A discrepancy between the
provided value (3.47 ft) and the value calculated using Equation 2 (3.39 ft =
122,404 cf/36,111 sf) was noted, please ensure that the information in the
submission is correct and consistent.
vi. Line 32 — Recalculate as needed.
vii. Line 34—The cleanout depth of the forebay is the distance from the permanent
pool surface to the top of the sediment storage zone in the forebay.
viii. Line 35 —The design volume of the SCM is the volume that can be stored above
the permanent pool surface elevation and below the invert of the lowest bypass
orifice/weir (temporary pool elevation).
ix. Lines 43 & 44—The depth of the forebay at the entrance/exit is measured from the
permanent pool surface elevation to the excavated bottom of the forebay near
either the entrance or exit of the forebay. The entrance of the forebay must be
deeper than the exit of the forebay and at least 6" of sediment storage must be
provided above the forebay entrance/exit.

x. Line 48— Per the provided detail, the orifice does not appear to draw down from
below the permanent pool surface (this is typically handled via a down-turned
elbow). It is strongly recommended to have the drawdown orifice drawdown from
below the permanent pool surface. It is noted that a trash guard is provided around
the orifice to prevent clogging.
Response: each line item on the wet pond page has been updated to be accurate and match the plans and
calculations.
d. Sand Filter Page:
i. Line 2— Please revise this item in accordance with the earlier comment. The
minimum required treatment volume should be based on the actual drainage area
to the SCM. Please revise as needed.
ii. Line 9—The provided details do not appear to indicate a drawdown orifice to
dewater the sand filters.
iii. Line 14—This item is required per General MDC 11.
iv. Line 18— Please provide the SHWT elevations from within the footprint of the
proposed SCMs.
v. Line 23—This item refers to the volume that can be stored above the excavated
bottom of the sediment chamber and below the invert of the lowest bypass
orifice/weir.
vi. Line 26— Please provide the stage-storage tables for the SCMs so this value can be
verified. This item refers to the cross-sectional area of the sediment chamber at the
excavated bottom elevation (Line 25).
vii. Line 27—This item refers to the distance from the excavated bottom of the
sediment chamber (Line 25) to the invert of the lowest bypass orifice/weir.
viii. Line 28—This item is Line 27 minus the depth of any permanent pool provided in
the sediment chamber.
ix. Line 30—This item refers to the volume that can be stored above the top of the
sand layer in the sand chamber and below the invert of the lowest bypass
orifice/weir. Storage provided within the sand layer is not included.

x. Line 31—This item refers to the excavated bottom of the sand chamber (i.e., the
lowest point of the sand chamber).
xi. Line 32 — Please provide the stage-storage tables for the SCMs so this value can be
verified. This item refers to the cross-sectional area of the sand chamber at the top
of the sand layer.
xii. Line 33—This item refers to the distance from the excavated bottom of the sand
chamber (Line 31) to the invert of the lowest bypass orifice/weir.
xiii. Line 34—This item refers to the distance from the top of the sand layer to the
invert of the lowest bypass orifice/weir.
xiv. Line 35—The bypass device would be the lowest orifice/weir in the outlet
structure. For example, for SCM 2, this would be the 4"x24" orifice @ elevation
576.82'.
xv. Line 36—This item refers to the type of bypass device listed on Line 35.
Response: each line item on the sand filter page has been updated to be accurate and match the plans and
calculations.
Thank you again for the review of this project. Please do not hesitate to reach out if you have any questions.
You can call me at the office [phone] or my mobile: [phone].
Thank you,
Bryan Linton, PE
[e-mail]