SW3230701_Response To Comments_20240621

T THOMAS
Imi HUTTON
June 20, 2024
NCDEQ- DEMLR
Attn: Jim Farkas
512 N. Salisbury Street, Office 640M
Raleigh, NC 27604
Re: Stewart's Grove Subdivision
#SW3230701
Wingate, NC
J-31540.0000
To whom it may concern:
This letter serves as acknowledgement that we have revised the previously submitted package to
address all comments below as follows:
General Issues
1. Prior Comment 1
"As designed, the project does not appear to capture and treat
sufficient on-site BUA in order for the project to meet Runoff Treatment (15A NCAC
02H.1002(43)). Per the application, the %BUA for the site is shown as 34.76% which
would result in approximately 6.33 ac of new BUA whereas the SCM is only capturing
& treating approximately 5.14 ac. Please ensure that the net increase in on-site 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 revise as needed."
Please complete the Drainage Areas Page of the Supplement-EZ Form so that this
information can be verified. Per the drainage area delineations provided in the
calculation booklet, all of the BUA appears to be captured in the SCM drainage
areas, we just need to be able to
verify this.
Supplement-EZ form updated to include Drainage Areas page.
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T THOMAS
HUTTON
2. Prior Comment 2
"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 153,370 sf
whereas the total amount of BUA allocated to the subdivided lots per the deed
restriction document is 153,390 sf. Please revise as needed."
Please complete the Drainage Areas Page of the Supplement-EZ Form so that this
information can be verified. Per the Application Form, the total amount of BUA
allocated to the subdivided lots is shown as 96,960 sf (88,640 sf + 8,320 sf = 96,960 sf)
whereas the deed restriction form indicates the total amount of BUA allocated to the
subdivided lots is 126,720 sf (35 lots @ 3,360 sf/lot & 3 lots @ 3,040 sf/lot). Please revise
as needed.
Supplement-EZ form updated to include Drainage Areas page. Application Form
corrected to match deed restriction form.
3. Prior Comment 5.a.
"Please add the following items to the plan set... Drainage area
delineation to the SCM. It is noted that a drainage area delineation is provided in the
calculations, however, per 15A NCAC 02H.1042(2)(g)(iv), the drainage area
delineation must be included in the main set of plans. Please revise."
This item was not provided.
Drainage area delineation to BMPs added to plan set. See sheet C3.10.
4. Prior Comment 6.a. —
"Drainage Area Page..."
Please complete the Drainage Areas Page of the Supplement-EZ Form so that this
information can be verified.
Supplement-EZ form updated to include Drainage Areas page.
5. Please be aware that DEQ considers the filtering layer of sand and storage provided above
the filtering layer of sand (in both the sediment chamber and sand chamber) to be a single
SCM, the sand filter and does not consider it to be two separate SCMs (sand filter & dry
pond). Please revise the submittal materials as needed.
Removed dry pond data from Supplement-EZ form and revised sand filter sheet.
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HUTTON
6. Please provide hard copies of all of the revised plan sheets. This item is required per 15A
NCAC 02H .1042(2)(g). NOTE: Only revised hard copies of plan sheets EC1.0-EC3.3 and C3.7-
C3.9 were provided.
All revised documents provided as part of this submittal.
7. Per the USGS topographic map for the area, there are surface waters located within the
project area (see attached image). Please ensure that this surface water area is accounted
for in Section IV, 6 of the Application and Sections IV, 7, 8, & 10 of the Application are revised
as needed (to exclude the surface water area). Please also ensure that this surface water
area is accounted for on Line 4 of the Cover Page of the Supplement-EZ Form and Line 2 of
the Cover Page is revised as needed (to exclude the surface water area). NOTE: The surface
water area of a stream is the area between the banks (please also ensure that the
vegetated setback is measured from this area and not just the stream centerline).
Section IV, Subsections 6-8, 10 updated to account for existing surface water area from
ponds and streams on site and to reflect the site layout. Supplement-EZ cover page updated
to reflect the corrected project area.
8. Please correct the following issues with the SCM design:
a. General:
i. Sand Filter MDC 1 - Please provide the SHWT elevation for this SCM.
SHWT testing by Southern Engineering did not find evidence of SHWT in the
vicinity of either SCM.
ii. Sand Filter MDCs 2 & 3- Please provide a stage-storage table for both the
sediment and sand chambers of the proposed SCM so that these MDC can
be verified.
Stage storage tables have been added to the stormwater management
report. See appendix J.
iii. Sand Filter MDC 8- Per the provided calculations, the filter media coefficient
of permeability is shown to be 3.5 ft/day which equals 1.75 in/hour. Sand filter
MDC 8 requires the sand filter to be maintained in a manner that results in a
drawdown rate of 2.0 in/hr at the sand filter surface. Please revise as needed.
The coefficient of permeability has been updated to reflect minimum criteria
of 2.0 in/hr.
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T THOMAS
Imi HUTTON
b. SCM 1:
i. While not required, it is strongly recommended to limit the drainage area of a
sand filter to no more than 5 acres (about 8.7 ac is draining to the SCM) and
to limit the percent pervious area draining to the sand filter (about 3.9 ac of
pervious area is draining to the SCM). You may wish to select a more
appropriate SCM for the site or use more, smaller sand filters for this site.
Noted. Due to the configuration of the site the sand filters as designed are the
only viable option for stormwater treatment.
ii. The provided minimum required treatment volume sizing/design calculations
do not correspond to the other submittal items. For example, the calculations
show a drainage area to the SCM as 8.547 ac (8.71 ac shown in the
Application), the calculations show a percent BUA for the drainage area to
the SCM as 65% (54.9%shown in the Application, etc... Please revise as
needed for consistency.
All documents have been revised as necessary to provide consistency.
c. SCM 2:
i. While not required, it is strongly recommended to limit the percent pervious
area draining to the sand filter (about 81% of the area draining to the SCM is
pervious). You may wish to select a more appropriate SCM for the site.
Noted. Due to the configuration of the site the sand filters as designed are the
only viable option for stormwater treatment.
ii. The provided minimum required treatment volume sizing/design calculations
do not correspond to the other submittal items. For example, the calculations
show a percent BUA for the drainage area to the SCM as 65% (19.1% shown in
the Application, etc... Please revise as needed for consistency.
SCM calculations revised for consistency.
iii. Per Part C-6 of the Manual, the entire surface area of the sand chamber
should contain sand. Please revise as needed.
Plans updated to reflect full surface area coverage by sand within the BMP
sand chambers. See sheets C3.18 and C3.19.
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T THOMAS
Imi HUTTON
9. Please correct the following issues with the Application:
a. Section IV, 1 - Please remove the references to dry ponds (see earlier comment).
Application updated to remove references to dry ponds.
b. Section IV, 4, 6, 7, &8- Please revise these values in accordance with the earlier on-
site surface water area comment. Line 4 should be the total property area, Line 6
should be the total on-site surface water area, Line 7 is equal to Line 4- Line 6, and
Line 8 will need to be recalculated (for a site with no existing BUA, [Percent BUA] =
[Proposed BUA] / [Total Project Area] (does not include surface water areas).
Application updated to reflect reductions in project area due to existing surface
waters.
c. Section IV, 10- For a subdivision project, the On-site Buildings/Lots line should
exclusively be used for BUA allocated to the individual lots (BUA allocated to
common areas, such as the roadway) should be shown in the other applicable lines).
Please revise as needed.
Tabulations for on-site buildings/lots updated to reflect BUA exclusively allocated to
each lot (pad areas and driveways).
10. Please correct the following issues with the Supplement-EZ Form:
a. Cover Page:
i. Lines 2 & 4-See earlier comments with regard to the project area and on-site
surface water area for this project. Line 2 should correspond to Section IV, 7 of
the Application and Line 4 should correspond to Section IV, 6 of the
Application.
Line items corrected to match with revised application.
ii. Line 22-See earlier comment with regard to dry ponds.
References to dry ponds removed.
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T THOMAS
HUTTON
b. Drainage Areas Page:
i. Please provide the table that is supposed to be included on this page of the
form (BUA accounting for the entire site and drainage areas). NOTE: This
spreadsheet uses macros to generate information based on the information
entered into the top part of this sheet. You need to enable macros and then
click on the "Click to load form" link to generate this table.
Drainage Area table completed and included in this submission.
c. Sand Filter Page:
i. Line 1 -These drainage area values should correspond to the drainage area
column on the Drainage Areas Page of the Supplement-EZ Form for the
drainage area to each SCM.
Drainage areas updated to reflect drainage area page.
ii. Line 2-See earlier comment with regard to the minimum required treatment
volume calculations for the SCM.
Values updated to reflect corrected minimum required treatment volumes.
iii. Line 18- Please provide this information (see earlier comment).
SHWT testing by Southern Engineering did not find evidence of SHWT in the
vicinity of either SCM.
iv. Lines 19-21 -The SCM details do not appear to reflect a closed bottomed
sand filter design (a closed bottomed sand filter requires an impervious liner
separating the sand filter from the surrounding in-situ soils). Please revise as
needed.
Form updated to reflect open bottom SCM design for both BMPs.
v. Lines 23, 26, 30, & 32- Please revise as needed in accordance with the stage-
storage tables that will be provided.
Lines updated for consistency with stage storage tables provided with this
submittal.
vi. Line 25-This item refers to the lowest excavated elevation of the sediment
chamber. For example, for SCM 1, the plans indicate that this elevation is
534.0' (532.5' is shown). Please revise as needed for each SCM.
Line item updated to reflect bottom of sediment chamber.
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Imi HUTTON
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
(Line 35). Please revise as needed for each SCM.
Line item corrected per guidance.
viii. Line 28-This item is Line 27 minus the depth of any permanent pool provided
in the sediment chamber (If there is no permanent pool in the sediment
chamber, this value will be the same as Line 27). Please revise as needed for
each SCM.
Line item corrected per guidance.
ix. Line 29-This item refers to the elevation of the top of the weir separating the
sediment chamber from the sand chamber. For example, for SCM 1, the plans
indicate that this elevation is 535.3' (539.5' is shown). Please revise as needed
for each SCM.
Line item corrected to match plans regarding sediment chamber berm
elevation.
x. Line 31 -This item refers to the excavated bottom of the sand chamber and
not the top of the sand/washed stone layer (it is used to determine the low
point of the system for determining SHWT separation). For example, for SCM 1,
the plans indicate that this elevation is 535.3' (539.5' is shown). Please revise as
needed for each SCM.
Line item updated to reflect lowest excavated point of SCM.
xi. 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.
Line item corrected per guidance.
xii. Line 34-This item refers to the distance from the top of the sand layer to the
invert of the lowest bypass orifice/weir.
Line item corrected per guidance.
xiii. Line 35-This item refers to the invert elevation of the lowest bypass device.
For example, for SCM 1, the plans indicate that this would be the weir at
elevation 536.0' (539.5' is shown). Please revise as needed for each SCM.
Line item corrected per guidance.
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T THOMAS
HUTTON
xiv. Line 36- Bypass device refers to any device that allows any stormwater runoff
to avoid the treatment provided by the SCM.
Line item corrected to reflect lowest bypass weirs.
xv. Line 37- Please clarify what is meant by this. What mechanism (weir, pipe
network, level spreader, etc...) causes stormwater from the sediment
chamber to enter the sand chamber as disperse flow?
The berm separating the sedimentation chamber from the sand chamber
shall be constructed of class B rip-rap to allow for the percolation of water
through the berm from the sedimentation chamber into the sand chamber
and across the filter surface.
d. Dry Pond Page:
i. Please remove the dry pond page (see earlier comment).
Removed.
11. Please correct the following issues with the O&M Agreement Form:
a. Please provide an original, signed & notarized hard copy of this form. This is required
per 15A NCAC 02H .1042(2)(j).
Original hard copy of the O&M form provided as part of this submission.
b. Please remove the references to dry ponds (see earlier comments).
Removed.
We look forward to receiving the approved certification for the referenced project to
allow us to proceed. If you have any questions,comments,or desire additional information, please
contact our office at [phone].
Sincerely,
THOMAS & HUTTON
Nestor Hernandez, PE
1020 Euclid Avenue I Charlotte, North Carolina 28203 1 [phone] I thomasandhutton.com