SW3191205_2020-01-20 State WQ Response Letter_2/11/2020

HensonFoley
Landscape Architecture I Civil Engineering
January 20, 2020
NC DELMLR
512 N. Salisbury Street
Raleigh, NC 27699-1612
Re: Windsong Subdivision
State project # SW3191205
HFI Project # 217053
Mr. Anen:
The following is a response to the comments on the review of the above referenced
project.
1. This project is in the Goose Creek watershed and thus must comply with the Goose
Creek Rules for stormwater management (15A NCAC 02B .0602). These rules require
the project to use stormwater controls to infiltrate runoff unless it can be proven by a
geotechnical investigation that it is not feasible on site.
RESPONSE: This design requirement is acknowledged. This requirement was discussed at
the beginning of the project and ksat testing was conducted. Attached, please find the
geotechnical report, early design plan sheet & email correspondence with Mr. Anen. The
overall project design and BMP / sand filter locations have changed but the underlying
bad soils still remain an issue. Based on these findings, we request exemption from the
infiltration requirement.
2. On Page 1 of the SWU-101 application, please provide the closest city and the zip
code of the project.
RESPONSE: The adjacent City, State & Zip code has been added to page 1 item 2.
3. On Page 2 of the SWU-101 application form, the applicant was listed as the
developer. Because the property is owned by the applicant, the box for property
owner should be checked.
RESPONSE: This has been corrected.
4. On Page 6 of the SWU-101 application, please have the applicant complete the
Applicant's Certification instead of the Property Owner's Certification. The Property
Owner's Certification is only required when the applicant is not the property owner.
The Applicant's Certification is required for all applications.
RESPONSE: The applicant has completed the "Applicant's Certification" portion.
Provided as part of this resubmittal is a scanned copy of the signature page. The client
will send the original signature to you directly.
5. Please submit a signed and sealed hardcopy of the Supplement EZ form. Please
ensure the information in the Supplement EZ form is complete and updated in
accordance with any revisions requested in this letter.
RESPONSE: The signed & sealed hardcopy is provided.
6. Please provide full size (at least 22 inches by 34 inches) copies of the pre -
development and post -development drainage areas.
RESPONSE: Full size hard copies of the requested plans are provided.
8712 Lindholm Dr, Suite 202A- Huntersville, NC 28078 - 704.875.1615 ph - 704.875.0959 fax
www.hensonfoley.com [e-mail]

HensonFoley
Landscape Architecture I Civil Engineering
7. Please provide the name of the individual signing the Deed Restrictions and
Protective Covenants Form at the top of the form.
RESPONSE: The applicants name has been added to the form.
8. The easements for each SCM must extend to the nearest public right-of-way
(General MDC 9).
RESPONSE: The BMP access easements have been relocated & extended to provide
connection to the proposed NCDOT ROW of Windsong Dr. See sheet C33.
9. Please provide a geotechnical investigation to show that the distance between the
lowest point of the sand filter system and the seasonal high water table is at least two
feet (Sand Filter MDC 1).
RESPONSE: The Estimated Seasonal High Water Table report is provided. It indicates that
there was no water encountered in any of the test pits nor any indication of ESHWT.
10. The sand filter must include a sediment chamber and a sand chamber. The storage
in the two chambers shall be equivalent. The sediment chamber can be oversized to
provide detention storage as long as there is sufficient storage volume in the sand
chamber to hold at least 50% of the design volume below the first outlet (Sand Filter
MDC 2 and 3). Please provide stage storage data for both chambers to verify this.
RESPONSE: The sediment & sand chambers for the 3 ponds have been revised to provide
approximate equivalent volumes. The sand & sediment chamber stage storage for the 1
year 24 hour event are provided in the calculation book (page 74-88) to show there is a
minimum of 50% of the discounted water quality volume storage. The discounted WQ
volume has been added to the BMP sand filter design calculation pages (calc book
page 3, 5 & 7).
Below is a quick summary for all 3 basins.
Pond 1:
Req. WQ Volume
12,945 cf
Discounted Volume
9,708 cf
50% of Discounted
4,854 cf
Provided Volume
5,209 cf @ elev. 553.50
3.5" Orifice Elev.
553.60
Pond 2:
Req. WQ Volume
6,653
cf
Discounted Volume
4,989
cf
50% of Discounted
2,495
cf
Provided Volume
2,603
cf @ elev. 558.40
3.5" Orifice Elev.
558.50
Pond 3:
Req. WQ Volume
4,761
cf
Discounted Volume
3,570
cf
50% of Discounted
1,785
cf
Provided Volume
1,946
cf @ elev. 553.65
3.5" Orifice Elev.
553.70
8712 Lindholm Dr, Suite 202A- Hunfersville, NC 28078 - 704.875.1615 ph - 704.875.0959 fax
www.hensonfoley.com [e-mail]

HensonFoley
Landscape Architecture I Civil Engineering
11. Please specify on the plans that the sand to be used for the sand chamber must
meet the specifications of ASTM C33 or the equivalent and revise the plans to have
the sand cover the entirety of the sand chamber bottom (Sand Filter MDC 6).
RESPONSE: The sand requirement within the BMP details has been revised to the ASTM C33
or equivalent.
12. Provide pdfs of all revisions, 2 hardcopies of revised plan sheets, and 1 hardcopy of
other documents. Pdfs must be uploaded using the form at:
https://edocs.deq.nc.gov/Forms/SW_Project_Submittal
RESPONSE: The revised PDF's have been uploaded and hardcopies provided.
If you have any questions, Please feel free to give us a call.
Sincerely,
Timothy D. Foley, P.E.
Vice President
HensonFoley
8712 Lindholm Dr, Suite 202A- Hunfersville, NC 28078 - 704.875.1615 ph - 704.875.0959 fax
www.hensonfoley.com [e-mail]