SW4231002_Response To Comments_20240208

CRUMPLER
Consulting Services, PLLC
DEMLR Post-Construction Stormwater Program
Brianna Holland
512 N. Salisbury Street, Office 625Y
Raleigh, NC 27604
Re: Stormwater Permit No. SW4231002
Dollar Tree—Welcome, NC
Response to Comments
1. Design Requirements for High Density Projects
a.The project does not appear to meet the requirement of Runoff Treatment (15A NCAC
02H .1002(43)). For a project to meet Runoff Treatment, the net increase in BUA must be
captured and treated in one or more primary SCMs. Per the Supplement-EZ, Drainage Areas
Page and the figures provided in the calculations package, it appears that not all of the net
increase in BUA is directed to the SCM. If it is not practicable to capture and treat all the
required BUA,the bypassed areas can be permitted as a low-density area (provided that the
bypass area meets the low-density requirements). Occasionally,there are situations where it is
not practicable to capture all the required BUA in an SCM and it is not possible to permit the
bypass areas as a low-density area, these situations require a variance/waiver in accordance
with 15A NCAC 02H .1003(6). Revise the package as necessary and indicate which of the options
is being pursued.
The bypass area has been calculated and will be conforming to the low density requirements.
All calculations, maps,and applications have been updated.
2. Off-site Drainage Area:
a. Per 15A NCAC 02H .1003(3)(b) any off-site areas that drain to the SCM must be
accounted for at their full build-out potential. This can be accomplished by having the
property owners enter into a legal agreement limiting the amount of BUA and
drainage area directed from the off-site property to the SCM or by assuming that the
off-site area is 100% BUA(its full build-out potential). Bypassing off-site drainage
area around the SCM is recommended. If the off-site area is not bypassed, or a legal
agreement reached, please revise the calculations, Supplement-EZ, and Application accounting
for the offsite area as 100% BUA. Please see additional information after the comments.
The offsite area previously shown at the ROW is being diverted by an berm and roadside ditch
in the existing conditions.These berms and ditches are to remain and therefore no offsite BUA
is accounted for.
3. 3. Project area/Percent Impervious:
a. It appears in the plan sheets that a portion of the stream is within the property boundaries.
Total project area shall be calculated to exclude the area between the banks of streams and
rivers/areas below the Normal High Water Line per the instructions given in the Application and
15A NCAC 02H .1003 (1) (c). Revise the Application and Supplement-EZ to account for the
surface water area. Clearly delineate the project area in the main set of plans if it is not equal to
the property area.
This is not a stream and a roadside ditch with a culvert. It does not appear on the NRCS Soils
or USGS Topo maps.The notation has been revised to show it as a roadside ditch.
2308 Ridge Road I Raleigh, NC 27612 I p: 919-413-1704 I e:[e-mail]

CRUMPLER
Consulting Services, PLLC
b. Per Section IV, 10, Impervious Areas Table,the total BUA should be 10,000 SF+22,000
SF+1,750 SF+700 SF+16,631 SF= 51,081 SF. If the off-site drainage area is not diverted, it will
need to be 51,081 SF+4,150 SF= 55,231 SF. Ensure that the existing BUA is not being
accounted for multiple times within the Supplement-EZ and Application. Either list the existing
BUA as "existing BUA to be removed" and list the proposed conditions in the other categories,
or keep the "existing BUA to remain" listed and only list the net increase in BUA in the other
categories.
The BUA has been revised and incorporated into the revised calculations.
c. Revise the project percent impervious area. Per 15A NCAC 02H .1003 (1) (a,b,):The
Project percent of impervious area can be calculated as:
(a) Project percent of impervious area = (Total Impervious Area/Total Project Area) X 100
If there is existing BUA on the site,there is the option of calculating project density as:
(b) Project percent of impervious area = (Total Built-Upon Area - Existing Built-Upon
Area)/(Total Project Area - Existing Built-Upon Area)
The BUA calculations has been revised.The existing is to be removed and replaced so it was
calculated using comment(a).
(i)Verify that the net increase in BUA(including non-diverted off-site area) is treated by
the SCM.
The net increase is be treated and shown in the sizing calculations of the stormwater report.
d.As required per the Application Section VI, 8o, delineate the drainage area of the entire
site and the drainage area of the SCM on the main set of plans. Cleary indicate the on-site and
off-site drainage areas so the values provided in the Application, Supplement-EZ, and
calculations can be verified.
The drainage areas have been shown on all plan sheets.
4. 4. Wet Pond
a. Per Wet Pond MDC 1,the volume of the main pools and the forebays should not include
the sediment storage zone since this portion of the pond is intended to be filled up with
sediment and can therefore not count towards provided storage volume. Please revise the stage
storage tables, associated volumes, and calculations (such as average depth, which will change
the minimum required surface area, etc.). Revise the Supplement-EZ accordingly. Per the plans
provided,the main pool bottom elevation on the stage storage tables should be 857.50, and the
forebay bottom elevation should be 859.00.
The elevations have been revised and Supplement-EZ revised.
b.The temporary pool elevation is determined by the elevation of the lowest bypass. Per the
plans, it appears that this is intended to be the top of the riser structure, which is 864.50. Please
revise this elevation, or the temporary pool elevation used in the calculations (864).The
provided temporary pool storage table seems to underestimate the volume by not accounting
for the volume associated with the top of the temporary pool elevation. Revise the draw-down
calculations when this volume is revised.
The elevations have been revised and Supplement-EZ revised.The draw-down calculation has
been revised.
c. Per the provided Hydraflow Rainfall Report, Raleigh IDF data was utilized please revise
to a more geographically appropriate station.
The IDF has been updated.
2308 Ridge Road I Raleigh, NC 27612 I p: 919-413-1704 I e:[e-mail]

CRUMPLER
Consulting Services, PLLC
d. Per Wet Pond MDC 6:The main pool shall be equipped with a vegetative shelf around its
perimeter.
There is a vegetative shelf shown on the plans.
e. Per Wet Pond MDC 11, 50 plants per 200 square feet of shelf area is required.The
Landscaping requirements note on the plan says 460 plants will be provided, but 65+61+57=
183 plants that were listed in the provided planting schedule.The plan view shows 460 plants
called out. Please confirm there is 1,840 SF of vegetated shelf.The 1,840 SF/200 SF=460
plants equation is unclear.
The planting schedule has been updated.
5. Consistency:
a. Clearly show the existing BUA within the project area, and within the drainage area to
the Wet Pond.The value 16,631 SF is consistent between the Application and calculations, but
is not consistent with the Supplement-EZ, and is not clearly verifiable within the package. It is
recommended to include a BUA accounting table with the drainage area maps (similar to the
one found in Section IV, 10) showing the size of the drainage area (with on-site/off-site areas)
and BUA allocation (amount and type) for the existing and proposed drainage areas.
The BUA has been updated to reflect. On the Wet Pond detail,the table has been added.
b. Revise the narrative to match the rest of the package.The narrative currently references a
dry detention basin, which is not a primary SCM.
The narrative has been updated.
c. Drainage Area 1 of the Application and the Wet Pond Column of the Supplement-EZ,
Drainage Areas Page is the drainage area that is draining to the SCM.The information provided
in these tables need to match. For example,the Existing BUA listed in the Application is 16,631
SF, but the Supplement-EZ lists 11,846 SF. Revise all items in these tables to match so that the
package can be more accurately reviewed.Values, such as the minimum treatment volume
required, cannot be confirmed without verifying the BUA values.
The application and Supplement-EZ has been updated.
d.The emergency spillway elevation is listed as 397.75 in the emergency spillway detail,
which appears to be an error.
The application and Supplement-EZ has been updated.
e.The O&M Agreement Wet Detention Pond Design Summary and the Supplement-EZ list
the temporary pool elevation as 862.41, which does not match the plans or calculations. Please
revise for consistency.
The O&M agreement has been updated.
6. Supplement-EZ:
a. Drainage Area Page, Line 9—The BUA does not appear to be on subdivided lots, so
please move these values to Line 10, "New BUA not on subdivided lots."
The application and Supplement-EZ has been updated.
b. Wet Pond Page, Line 17—Per 15A NCAC 02H .1050 (16),the SCM must be designed by
an NC licensed professional, please revise.
The application and Supplement-EZ has been updated.
c. Wet Pond Page, Line 35—For a wet pond,the design volume is the amount of storage
that is provided in the wet pond above the permanent pool surface and below the
elevation of the lowest bypass weir/orifice in the outlet structure (temporary pool
elevation) and must be at least as large as the minimum required treatment volume.
2308 Ridge Road I Raleigh, NC 27612 I p: 919-413-1704 I e:[e-mail]

CRUMPLER
Consulting Services, PLLC
Please revise accordingly.
The application and Supplement-EZ has been updated.
d. Wet Pond Page, Line 40—The drawdown time is the amount of time to drawdown the
design volume provided in Line 35.
The drawdown time has been added to the sizing calculations.
7. Please show the required vegetated setback from surface waters in the main set of plans.
This item is required per 15A NCAC 02H .1042(2)(g)(iii). Per 15A NCAC 02H
.1017(10),the vegetated setback width from surface waters is 30 ft. Revise the
Supplement-EZ, Cover Page, Line 7 accordingly.
This is not a stream and a roadside ditch with a culvert. It does not appear on the NRCS Soils
or USGS Topo maps.The notation has been revised to show it as a roadside ditch. So no
vegetated setback required.
8. The narrative located within the calculations references utilizing buy down methods for
nitrogen loading rates. Please provide proof of nutrient offset credit purchase if nutrient
offset credits are being used for this project (15A NCAC 02B .0711(5)(d)).
No buydown required and removed from narrative.
9. Per 15A NCAC 02H .1050 (4), provide engineering calculations demonstrating that the
inlets and outlets of the SCM are protected from erosion resulting from stormwater
discharges during peak flow from the 10-year storm.
These calculations have been added to the stormwater report.
10. Per 15A NCAC 02H .1003 (5), provide calculations demonstrating that the outlets of the
site do not cause erosion downslope of the discharge point during the peak flow from the
10-year storm event.
The dissipator pad calculations have been added to the stormwater report.
11. Per 15A NCAC 02H .1050 8 and 9, maintenance accesses shall: have a minimum width
of ten feet; not include lateral or incline slopes that exceed 3:1 (horizontal to vertical);
and extend to the nearest public right-of-way.The entire SCM shall be shown and
labeled within the easement, including the emergency spillway.These are required to be
shown on plans per 15A NCAC 02H .1042 (2) (g) (vi).
The easement has been added to the plan set.
12. As the temporary pool drains, the rate of discharge decreases and this does not appear to
be accounted for in the drawdown calculations resulting in an undersized orifice. (We
recommend using a third of the driving head to calculate the orifice drawdown rate to
account for this decreasing rate of discharge.) Please revise as needed.
The orifice has been updated in the sizing calculations.
13. Please initial all provided items in the Application, Section VI. If an item is not
applicable, please indicate "N/A".
The revised pages to the application have been updated.
2308 Ridge Road I Raleigh, NC 27612 I p: 919-413-1704 I e:[e-mail]

CRUMPLER
Consulting Services, PLLC
14. Please ensure the electronic repository is complete. Refer to 15A NCAC 02H .1042(2)
and the checklist provided in the application for the list of documents required for a
complete permit application. It was noted that the following were not included in the
electronic repository:
• A copy of the most current property deed. (Required per the Application Section
VI, 10)
• Documentation from the NC Secretary of State or other official documentation,
which supports the titles and positions held by the persons listed in Contact
Information, item la and 2a per 15A NCAC 2H.1003(e).The corporation or LLC
must be listed as an active corporation in good standing with the NC Secretary of
State, otherwise the application will be returned.
http://www.secretary.state.nc.us/Corporations/CSearch.aspx
The plans have been uploaded to the website and hard copies provided to the office.
15. Provide PDFs of all revisions, 2 hardcopies of revised plan sheets, 1 hardcopy of other
documents, and a response to comments letter briefly describing how the comments have
been addressed.
The plans have been uploaded to the website and hard copies provided to the office.
2308 Ridge Road I Raleigh, NC 27612 I p: 919-413-1704 I e:[e-mail]