SW4211101_Response To Comments_20220110

Green Mountain Engineering, PLLC Civil Engineering Consultants
i
To: Jim Farkas, Environmental Engineer
Address: 512 N. Salisbury St. 1612 Mail Service Center Raleigh, NC 27699-1612
From: Jordan Young, P.E. Green Mountain Engineering, PLLC
Date: December 20, 2021
Re: Barrow Farms- Phase 1 & 2
Messages
Jim,
Please see responses to the Stormwater comments on December 20, 2021.
It is recommended to place the proposed water main underneath the stormwater
pipes so that the stormwater piping does not need to be so deep and the stormwater road
crossings can be handled with culverts as opposed to pipe networks (similar to how STP-7
is situated). Using this design approach, it appears as though pipes STP-2, STP-3, & STP-6 can
be set up as culverts and pipes STP-1, STP-4, STP-5 can be replaced with swales (there should be
sufficient room in the drainage easement to place these swales and the grading should not be too
severe since the culverts will be a lot closer to the surface than the current pipe network).
Formally known pipes STP-1, 4 & 5 have been removed and replaced with swales. Formally
known pipes STP-2 & 6 have been converted to culverts and brought closer to the surface with
waterlines dipping under these pipes with 24" of separation.
2. The provided project coordinates (360 11' 10.13" N, 800 06' 32.02" W) does not correspond to
the project location, it is about 2,000 ft off (Section I, 4 of the Application). Please revise.
I have updated the project coordinates to 360 10' S 1.24"N, 800 06' 50.76"W
3. Please specify which additional permits are required for this project (Section II, 4). I have added
the Sediment/Erosion control permit is required and 27.00 ac of disturbance.
4. Since the Applicant is also the Property Owner, Section III, 2 of the Application is not
required to be filled out. Please revise as needed. Section III, 2 has been removed from
application.
5. This project does not appear to have a vested right claim (Section IV, 2a). Please revise. Section
IV, 2a has been removed from the application.
6. This project does not appear to be located within the Cape Fear River basin (Section IV, 3).
Please revise. Section IV, 3 has been revised to Roanoke River basin.
7A Wendy Court - Greensboro, NC 27409 - [phone]

Green Mountain Engineering, PLLC Civil Engineering Consultants
7. There appears to be a calculation error in the percent impervious area calculation
(Section IV, 8). The percent impervious area shown in this part of the Application should be
consistent with the values Shown in Section IV, 10. Percent impervious area can be
calculated using the methodology outlined in 15A NCAC 02H .1003(1). The percentage
was actually correct as 12.42% but the numbers in the table were slightly off. Here is the
calculation included in this application (total impervious area/total project area)
184,543sf/1,485,396 sf= 12.42%.
8. The project area does not appear to directly drain to Belew Creek (Section IV, 10).
Please revise. This information can be found (along with the river basin) at the following
web address: Section IV 10 has been revised to Left Fork Belews Creek and Stream Class C
Index number 22-27-5.
9. Please show the areas in the top half of the table in Section IV, 10 of the Application in
square feet instead of acres. All areas have been revised to square footage.
10. Since this project is being permitted as a low -density project, the "drainage area" for the
project is the total project area (as explained in Section IV, 9). Please adjust the Total
Drainage Area and Off -Site Drainage Area values to reflect this. Project drainage areahas
been revised to 1 drainage area as the total project area 1,485,396 sf
11. The On -Site Buildings/Lots value is the total amount of BUA allocated to the individual
lots. Per the deed restriction document, there are 33 lots that are each allocated 3,599 sf
which would result in an On -Site Buildings/Lots value in the table of 118,767 sf (and 0 sf
value for the On -Site Parking since this item would refer to any parking area in the
common areas). "On -site buildings/lots" has been updated to 118,767 sf (3,599 per lot). "On -site
parking" has been revised to 0 sf.
12. Since there are no off -site areas for a low -density project (see earlier comment) Section
IV, 11 is not required. "Offsite drainage area" has been revised to 0 sf. Section IV, 11 has been
removed from application.
13. The provided calculations are insufficient (Section V1,7):
a. Please provide a source for the 10-year rainfall intensity (i) values used in the
provided calculations. If you are using time of concentration (tc) values that are
greater than 5 minutes, please also provide calculations showing how these
values were determined. I have included the NOAA rainfall intensity data table
downloaded from the NOAA rainfall data website. Calculations use the 10-yr, 5-
minute data which is 6.84 in/hr for this project location.
b. Please provide the Manning's roughness coefficient (n) values used for these
calculations (back calculating the Manning's roughness coefficient for swale 1
7A Wendy Court - Greensboro, NC 27409 - [phone]

Green Mountain Engineering, PLLC Civil Engineering Consultants
based on the provided swale geometry, flow rate, normal depth, and velocity
results in a Manning's value of approximately 0.24 which seems much too high)
0.24 was used for the manning's number based of TR-55 dense grass ground
cover. Using Manning's equation based off the proposed channels dimensions,
the average manning's number was 0.10 and comparing to "Manning's n for
channels (Chow, 1959)": "Channels -dense grass and weeds" has a range of 0.05-
0.12 my average 0.10 manning's number seems to be correct, falling in this
range. As you can see on sheet C-6.01 all channel calcs now use 0.10 for the
manning's number.
c. Please provide calculations for all proposed vegetated conveyances (see
attached map of excluded vegetated conveyances. It is unclear whether or not
the swale downstream of STP-7 is its own swale or if it is a separate swale).
I have added a plan sheet named vegetated conveyances drainage areas number
C-6.01 which include the channel calculations and numbered channels.
NOTE: Swales or vegetated conveyances that discharge to wetlands should do so
at no more than 2.0 fps to be considered as non -erosive. The highest velocity
from these channel calculations 1.99 fps
14. The provided details of the vegetated conveyances are insufficient (Section V1,81). Please
clearly show the bottom width of the vegetated conveyances on the detail (the
calculations show that the vegetated conveyances have a bottom width of 2 ft but the
detail shows a "V" shaped ditch) and please specify the grass type to be used in the
vegetated conveyances (This is required to determine the maximum allowable velocity
within the vegetated conveyance per the table in Part C-11 of the Design Manual). I have
revised the street cross section on sheet C-0.00 & 3.00 to show a road side swale with a flat
bottom calling out varying widths. Also, on sheet C-6.01 I have noted the types of acceptable
grasses planted in the vegetated conveyances. I listed all of the types of grass and left it up to
the contractor because all of the velocities are below 2.0 fps
15. Please delineate the drainage areas to the vegetated conveyances in the main set of
plans (Section VI, 8o). The provided drainage area delineation on plan sheet C-6.0 are
delineated for the yard inlets, not the vegetated conveyances (there is some overlap
between these, but they are not necessarily the same) and plan sheet C-3.0 (the plan
sheet with the vegetated conveyances labeled) does not contain drainage area
delineations. Please revise. I have added sheet C-6.01 with the drainage areas draining to all
9 channels. I also updated the channel calculations and moved them to this sheet to keep
everything together.
16. Since the Applicant is also the Property Owner, Section IX of the Application should not
be signed. With your permission, I can cross out the signature on the original signed hard
copy that I have and you can edit the electronic file. If that is not satisfactory, please
provide a revised signature page. I will not include this page in this resubmittal. Could you please
cross out the signature on this page. I will update the application on the electronic file.
7A Wendy Court - Greensboro, NC 27409 - [phone]

Green Mountain Engineering, PLLC Civil Engineering Consultants
17. Please correct the following issues with the Supplement-EZ Form:
a. Drainage Areas Page:
i. Lines 5-7 — Please use square feet instead of acres for these values. These
values have been updated
ii. Lines 9 & 10 — These items do not correspond to the values shown in the
table in Section IV of the Application. Please revise. These values now
match section IV of the application, which also has been updated.
iii. Line 12 — Please include this item. This is a breakdown of the common
area BUA (Line 10) by type. The items in Line 12 should add up to Line 10.
I have added the area of the proposed BUA inside the common areas
65,776 sf from the roadway.
iv. Please fill out the LD 1 column. For this project, it will be the same as the
entire site column. I have filled out the LD 1 column of this table.
b. Low Density Page:
i. Line 4 — Please include the maximum side slopes of the vegetated
conveyances. This line does not format properly so the information
should be entered in Line 15 (additional information). I have made a note
under line 15 "additional information" that the side slopes of vegetated
conveyances are 3':1'.
ii. Lines 6-10 — Please complete these items if applicable. I have noted that
items 6-10 are not applicable because there are no curb outlet systems
proposed.
iii. Please include all vegetated conveyances and swales in the swale table.
have updated this table including all 9 swales.
Please let us know if you have any questions, comments, or require additional information. I
can be reached via email Jordanggreenmountainengineers.com or by phone [phone])
Best Regards,
Jordan Young
7A Wendy Court - Greensboro, NC 27409 - [phone]