SW6191205_2020.01.08 resp letter to NC DEQ SWM_1/9/2020

XAI
WOOLPE PT
DESIGNGEOSPATIAL INFRASTRUCTURE
January 8, 2020
Mr. Corey Anen
Environmental Engineer
NC DEQ Stormwater Program
512 North Salisbury Street / 1612 Mail Service Center
Raleigh, NC 27699-1612
RE: SOF Dining Facility, Aberdeen Training Facility
Fort Bragg, NC
Woolpert Project No. 78530
Stormwater Permit No. SW6191205
Mr. Anen,
In response to the comments sent via email dated Friday, December 20th, 2019 please find attached
the revised plan sheets. For ease of reference, we have rewritten your comments followed by our
response in italics.
A soil investigation to determine the in -situ hydraulic conductivity is required within the
footprint of each infiltration system [15A NCAC 02H .1051(1)]. Please provide a soil test within
the footprint of the northwest infiltration system (listed as Infiltration Area 1 on Sheet CG100).
RESP: A supplementary test in the northwesterly portion of the site was completed in December.
The report, which is dated December 201h has been added to the appendices of the storm water
management report. Pursuant to our phone call on January 81h, the infiltration rate for the
Northwesterly basin is directly taken from the supplemental report whilst the rate from the
larger basins has been maintained at a rate much less than the test results. Said revisions have
been incorporated into the routing computations of the report.
Please provide design calculations and specifications for the riprap protection for each inlet and
outlet to show that there will not be erosion during the peak flow from the 10- year storm event
[15A NCAC 20H .1050(4)]. RESP: The outlet pipes associated with this project are from the roof
drains. For sizing purposes, the roof drain with the largest contributory area has been added to
Appendix H.2. This had been errantly omitted in the prior version of the storm water
management report. The rip rap sizing, based upon the computation from App. H.2, is found in
Appendix J.2. The apron size is identified by keynote 6 on sheet CG100 and the detail found on
sheet C-502.
Please provide a detail of the at -grade infiltration systems including all elevations and overflows
or bypass devices for inflow volumes in excess of the design storm in accordance with 15A NCAC
02H .1050(5). RESP: The storm water management system is designed to retain and infiltration
the 951h percentile storm event as required by the Energy and Independence Security Act. As
such, the design exceeds the requirements for storm water quality and retains the entirety of the
1 year, 24-hour storm event. For reference, the computations for the 10 year and 25-year storm
events are included. The top of the curb and inlet number 1 serve as the overflow

January 811, 2020
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devices/mechanisms for the northerly infiltration basin. Storm structure 9 serves as the primary
overflow mechanism for the northwesterly infiltration basin. The top of the flume and sidewalk
serve as the secondary mechanism for the same area. The "elevated invert" leading to inlet
number 8 serves as the overflow device for the underground detention area.
4. Please add a note to the grading sheet or SCM details that every SCM impacted by
sedimentation and erosion control during the construction phase shall be cleaned out and
converted to its approved design state 15A NCAC 02H .1050(7). RESP: A notes has been added
to sheet C-502 with reference on sheet C-501.
Please submit a complete signed and sealed Supplement EZ form. The form can be found on the
Stormwater Design Manual website. RESP: The Supplement forms are enclosed. Note the
worksheet for the basin in the Northwest corner of the site indicates that the size is too small.
However, the basin is connected to the underground detention in the Southwest corner of the
site. Sheet CG100 Note 10 shows the 15" storm drain pipe entering the underground detention
system at invert 465. Detail sheet C-503 lists the invert at 465.5. Please correct the discrepancy.
RESP: Thank you for catching this errancy. The invert has been corrected to +465.00.
6. The calculations for the northern infiltration area, listed as Infiltration Area 2 on Sheet CG100,
use an area of 1890 sf, whereas the plans show the area as 890 sf. Please revise the calculations
to use the proper surface area. RESP: Thank you for catching this typographic error. The correct
and required area is 1,890 SF. The note has been corrected on sheet CG100.
7. The storage volume calculations for the underground system use V of stone media below the
perforated pipes, but the detail on Sheet C-503 show only 6". RESP: Please correct the
discrepancy. RESP: The detail has been corrected accordingly. The intent is to provide 1'.
8. The storage volume calculations for the underground system appear to under calculatethe
storage in the stone layer by a factor of 2. RESP: The computation has been corrected.
9. Provide 2 hardcopies of revised plan sheets, and 1 hardcopy of other documents. A PDF of each
must be uploaded using the form at: https://edocs.deg.nc.gov/Forms/Sw Proiect Submittal. RESP:
Acknowledged.
Should you have any questions or need additional information, please feel free to contact our office.
Sincerely,
Woolpert
Gregory Harnish, PE
Project Civil Engineer
cc: Kenneth McMillan, Lee Ward, Zachry Nichols, Joseph Bissaillon
(all via email)
G:\DE\Clients\Balfour Beatty Construction\70229 - DFAC and Starship\CorrespondeNCe\DSP 2 DHEC response letter.doc