SW3211201_Response To Comments_20220121

NCDEQ Stormwater
Response to Comments
Date of Comments: January 19, 2022
Date of Response: January 21, 2022
This project is located within the Sixmile Creek watershed which is subject to the Goose Creek
Watershed Rules (15A NCAC 02B .0602). These rules stipulate that, "Development and
redevelopment shall implement stormwater management measures that promote infiltration of
flows and groundwater recharge for the purpose of maintaining stream base flow." Please
provide an explanation of how the selected SCM promotes infiltration of flows and groundwater
recharge. If it is not practical to use an SCM that promotes infiltration of flows and groundwater
recharge for this site, please provide an explanation for why it is not practical to do so.
Response: This project does promote infiltration of flows and groundwater recharge
for the purpose of maintaining base flow. The soils on this site are all class B. This means the soils
have less runoff, and are much better at recapturing water and bringing it into the ground. Also, nearly
all of the proposed developed areas on this site are within the drainage area of the sites wet pond. This
limits the amount of runoff from the site. Furthermore, the proposed wet pond does not have a liner and
would allow some water to infiltrate into the soil and contribute to the groundwater recharge. Finally,
this project has a landscape plan and a BMP planting plan, which proposes the planting of a wide
range of street trees and plant species within the wet pond. This helps capture stormwater and reduce
the total runoff from the site. We believe all these factors help contribute to the infiltration of flows and
groundwater recharge, and satisfies the Goose Creek Watershed Rules.
2. The percent imperviousness of the project area is shown as 16.47% (Section IV, 8 of the
Application) and as 11.58% (Supplement-EZ Form, Drainage Areas Page, Entire Site Column,
Line 18).
Response: The Supplement EZ form had the value of 11.58% due to the inclusion of
offsite drainage area. However, now the drainage area for the Supplement EZ form is limited to just the
projects property. Now both forms have the 16.47% impervious value.
3. The BUA allocated to the individual lots is shown as 109,900 sf (Section IV, 10, "On -site
Buildings/Lots" Line of the Application) and as 199,722 sf (Supplement- EZ Form, Drainage
Areas Page, DA 1 Column, Line 9).
Response: The BUA allocated for the lots in Section IV was only accounting for the
building PADS, and not the total BUA on the lots; this has now been corrected. On the Supp-EZ form,
the 199,722 sf has been recalculated and corrected. Both forms now have the value of 168,106 sf of
BUA on lots within DA1.
4. The BUA allocated to non -subdivided roadways is shown as 104,036 sf (Section IV, 10, "On -
site Streets" Line of the Application) and as 95,618 sf (Supplement- EZ Form, Drainage Areas
Page, DA 1 Column, Line 12, Roadway).
Response: The value on the Supp-EZ form was not the correct value. Now both
forms show 104,036 sf.
5. The BUA allocated to non -subdivided parking is shown as 27,364 sf (Section IV, 10, "On -site
Parking" Line of the Application) and as 0 sf (Supplement-EZ Form, Drainage Areas Page, DA 1
Column, Line 12, Parking).
Response: The 27,364 sf value shown on the SWU-101 form was representing the
BUA area for driveways. However, now this value has been corrected to be 0 sf since there's no
parking areas in this project. Both forms now show 0 sf for parking.

NCDEQ Stormwater
Response to Comments
Date of Comments: January 19, 2022
Date of Response: January 21, 2022
The BUA allocated to non -subdivided sidewalks is shown as 29,775 sf (Section IV, 10, "On -site
Sidewalks" Line of the Application) and as 8,705 sf (Supplement-EZ Form, Drainage Areas
Page, DA 1 Column, Line 12, Sidewalk).
Response: The value on the Supp-EZ form was incorrect. Both forms now show
29,775 sf for sidewalks within DA1.
7. The BUA allocated to non -subdivided "other" is shown as 32,970 sf (Section IV, 10, "Other on -
site" Line of the Application) and as 0 sf (Supplement-EZ Form, Drainage Areas Page, DA 1
Column, Line 12, Other). Please also clarify what this other BUA is.
Response: The "other" BUA values have been corrected to show 2,128 sf. This BUA
is the area of driveways located in the road ROW's. Both forms now show 2,128 sf.
8. Cover Page: Line 7 — Per the Goose Creek Watershed Rules, riparian buffers are required within
200 feet of waterbodies within the 100-Year Floodplain and within 100 feet of waterbodies that
are not within the 100-Year Floodplain (15A NCAC 02B .0605). NOTE: The buffer requirements
for the Goose Creek Watershed Rules are implemented by the Division of Water Resources
(DWR).
Response: The previous value of 50 ft was incorrect. The correct value of 100 ft is
now shown.
9. Drainage Areas Page: Entire Site Column, Off -site Area. Please clarify what the off -site portion
of the entire site is. Typically, there are no off -site portions to the entire site since the entire site is
comprised of the entirety of the site (The "drainage area" of the entire site is the project area).
Response: This site has a stream that originates offsite and runs through the property.
The pre -post analysis includes drainage -area that's offsite. This was the offsite drainage area shown
on the Supp-EZ form. However, after the conversation with NCDEQ, the offsite drainage area is no
longer included on the Supp-EZ form. The Off -site drainage area value is now shown as 0 sf.
10. Wet Pond Page: Line 5 — This value refers to the vegetated side slopes of the SCM (required to
be 3:1 or flatter per General MDC 3).
Response: The 2:1 value shown was incorrect. The vegetated side slopes of the SCM
are 3:1, and the Supp-EZ form now shows this corrected slope.
11. Wet Pond Page: Line 8 — The outlet structure functions as an overflow/bypass for flows in
excess of the design volume.
Response: Noted; this line has been corrected to show "yes".
12. Wet Pond Page: Line 35 — See latter comment about the design volume for this SCM.
Response: This value has been changed from the 300,000+ cf. It now shows the
water volume stored during the 10-year storm event, which is 81,757 cf.
13. Wet Pond Page: Lines 36 - 39 — Per the plans, the outlet for this wet pond is the 3"

NCDEQ Stormwater
Response to Comments
Date of Comments: January 19, 2022
Date of Response: January 21, 2022
drawdown orifice, not the weir.
Response: These lines on the Supp-EZ form have been corrected to show the 3"
orifice as the outlet for this pond.
14. Wet Pond Page: Line 48 — Per the plans, the drawdown orifice draws down from belowthe
permanent pool elevation.
Response: This line has been corrected to show "yes".
15. Using the provided stage -storage table, the minimum required treatment volume, 45,637 cf,
would pond at an elevation of approximately 683.56 (The stage -storage table shows the
cumulative storage volume at elevation 683.5 of only 43,549 co which is above the invert of the
bypass weir located in the outlet structure (24" x 12" weir at elevation 683.5). Strictly speaking,
this is allowable and not against the MDCs for a wet pond, however it is a bad design practice
and goes against the spirit of the rules since the design volume of the wet pond should be
stored below any bypass devices and allowed to be drawn down via the drawdown orifice. This
is even more apparent when the chosen design volume, 303,318 cf, is used. About 80 percent
of this design volume is drawn down by the weir in the first couple of hours while the remaining
volume is slowly drawn down by the orifice in a couple of days (This is acceptable for quantity
management but doesn't really meet the intent of Wet Pond MDC 7). You are not required to
change the weir elevation (since this "intent" is not specified in the MDC and therefore non -
enforceable), but you should not use such a large design volume, especially since you are not
required to provide any additional treatment in excess of the 45,637 cf minimum required
treatment volume.
Response: This design volume has been changed from the 303,318 cf. It now shows
the water volume stored during the 10-year storm event, which is 81,757 cf.