SW6200101_Reply_09March2020_3/9/2020

Ft Bragg SOF Civil Affairs TEMF – PN69552
Stormwater Permit No: SW6200101
Stormwater Comments with Replies
Stephen Curry, P.E.
ACC / Mason & Hanger
March 9, 2020

1. Please submit full size plan sheets (minimum 22 inches by 34 inches) [15A NCAC 02H .1042(g)]. Only
the following sheets are required:
a. V-101
b. CG101 – CG113
c. CG 750 & 751
d. LP110 – LP 113

Reply: Concur, the sheets listed shall be resubmitted in the next submittal along with the following
sheets that had revisions: CG510, CG511, and the Wet Pond #1 calculations

2. Please delineate all wetlands on site or add a note that none exist with the name and qualifications of
the person/entity making the determination [15A NCAC 02H .1042(g)(iii)].

Reply: Concur, a note has been added to sheets V-101 and CG101-CG113 stating there are no wetlands
within the project construction limits or project boundary as per coordination with Ft Bragg DPW
Environmental. I also included a point of contact, Kenny McMillan, with phone number and email
address.

3. The seasonal high water table elevation for the bioretention cell is provided as El. 230, consistent
with a 2016 boring (B-5) conducted by Froehling & Robertson, Inc. (according to Appendix I of the
submitted geotechnical report). However, according to the report titled “Seasonal High Water Table
Determination and Hydraulic Conductivity Testing” by Three Oaks Engineer, dated March 27, 2019,
borings B-5 and B-6, which are in the area of the bioretention cell, show the seasonal high water table to
be 72 and 40 inches below the surface, respectively. Assuming that these depths from the existing
ground surface (approximately El. 242 or 243 based on the submitted existing grading plans), the
seasonal high water table is actually in the range of El. 236-240. This would not provide the separation
from the seasonal high water table required by Bioretention MDC 1. Please provide justification for the
use of the less conservative value.

Reply: You are correct. I overlooked the SHWT chart and went straight to the boring logs, B-5 and C-7 to
be specific. But, on previous projects in the vicinity of the Civil Affairs TEMF project, we have had issues
with SHWT and bioretention pond design. To ensure the bioretention basin doesn’t stay saturated, we
have included an 8-inch perforated piping system in the bottom of the pond that drains to the riser. To
somewhat help, refer to boring C-7. We are removing approximately 5-ft of the clayey silty fine to
medium sand and replacing it will the bioretention cell. Please see the attachment to the comments that
compile the geotech information pertinent to this comment. Overall, to my knowledge, Ft Bragg has
had good performing bioretention ponds using the perforated piping system. If we need to set up a call
to discuss in further detail, we will be happy to accommodate.

4. Please specify that the sod used on the bioretention cell shall be a non-clumping, deeprooted species
and that it shall not be grown in clay (Bioretention MDC 10).

Reply: Concur, general note added to sheet LP110 – LP113 stating sod shall be of type Zoysia, non-
clumping, and ensure that the species is deep-rooted and not installed directly on top of an
impermeable layer such as clay. Refer to General Note 7 on the Landscape Plan sheets.

5. Please address the following issues with regard to both wet ponds:

a. On the wet pond details, please specify that the slope of the vegetated shelf will be no
steeper than 6:1 (Wet Pond MDC 6). Please also specify the bottom and top elevations of the
vegetated shelf.

Reply: The design criteria for the vegetated shelves for both of the wet ponds have been
verified at the elevations shown in the stormwater report. 239’-240’ for Wet Pond #1 and 238’-
239’ for Wet Pond #2. Both are 6-ft wide and no steeper than 6:1. Although, sheets CG510 and
CG511 do need further information instructing the Contractor the elevations of the vegetated
shelves. Refer to sheet CG510/511 for additional information.

b. The drain time for the wet ponds was calculated for the maximum storage volume in the wet
ponds rather than the water quality volume. The drain time must be between two and five days
for the water quality volume only (Wet Pond MDC 7).

Reply: Error on my part. Wet Pond #1 should drawdown between the elevations 240 – 241.50,
or from the drawdown orifice to the top of the riser, not top of rise to emergency spillway. We
will revise the Wet Pond #1 Drawdown Time calculations and include in the revised file. The
revised drawdown time is 2.1 days. I checked Wet Pond #2 and it is correct in drawing down
from the orifice to the top of riser.

c. Not enough plants are specified for the vegetated shelf to meet the requirement of 50 plants
per 200 square feet of shelf area (Wet Pond MDC 11).

Reply: The vegetated shelf has been hatched and the plantlist revised to match the approved
plants in Wet Pond MDC 11, Table 3. Also, the plant quantities have been revised to meet the
50 plants per 200 square foot. Additional notes regarding the vegetated shelf have been added
for clarification to the Contractor. Wet Pond #1, VS area 2,550 sf. Wet Pond #2, VS area 8,725
sf.

6. The calculations for Wet Pond 1 use a contour area much smaller than that shown on the plan for El.
240.

Reply: The correct contour area for the 240 elevation is 11,354sf rather than the incorrect 9,917 sf. I
checked the area of the other contours and they were correct. This changes the provided volume from
38,241 cf to 38,959 cf. I think the best option is to resubmit the Wet Pond #1 calculations in its entirety.
Although the change is minimal, everything should be consistent.

7. Please double check the scale bars on the plan sheets. It appears that the scale bars on at least the
grading sheets are incorrect.

Reply: We have double checked all of the scales and can’t find the issue. The scale is for full size (22x34)
drawings and would be half that on half size (11x17) drawings. That is all I can think of. Maybe we can
discuss further to resolve. Unless, the folks we have printing accidently printed the sheets on 24x36.

8. 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

Reply: Concur. Revisions to be uploaded and hard copies send as per comment.

Large TEMF SHWT and KSAT Testing March 27, 2019
Three Oaks Job #19-702 2
RESULTS

Soil Series and SHWT Determinations
A soil series determination was attempted by comparing the soil boring profile descriptions to the
NRCS Official Series Description (OSD) and the results listed in Table 2. All soil borings were
representative of the Faceville soil series.

Soil characteristics indicative of a SHWT (redox concentrations and depletions) were observed at all
six boring locations and the depths shown in Table 2. Full soil profile descriptions are attached.
Table 2. Soil Series Determination, and SHWT Depth
Soil
Boring
Soil Series
Determination
SHWT
(in. below surface)
B1 Faceville 82
B2 Faceville >136
B3 Faceville 73
B4 Faceville 70
B5 Faceville 72
B6 Faceville 40

Hydraulic Conductivity Measurements
KSAT tests were completed in the most limiting soil horizon within two feet of the SHWT and the
results are listed in Table 3 below. It should be noted that KSAT values only represent the infiltration
rate within the tested soil horizon and cannot be applied to other soil horizons with differing soil
properties (texture, structure, consistence, mineralogy, etc.).

Table 3: Hydraulic conductivity tests results parameters
Test # Soil Boring # Horizon/
Texture Test Depth (in) Measured KSAT (in/hr)
1 B1 BC1 / C 76 0.0114
2 B2 C / SL 110 0.4533
3 B3 Bt / C 56 0.0483
4 B4 Bt2 / C 62 0.1074
5 B5 BC1 / SCL 65 0.1791
6 B6 BC1 / C 36 0.0231

CONCLUSIONS

The findings presented herein represent Three Oaks’ professional opinion based on our soil
investigation. Soil characteristics indicative of a SHWT was observed at all six boring locations.
KSAT tests were conducted at each boring location in the most limiting soil horizon that occurs within
2-feet of the SHWT.

Due to the inherent variability of soils to change over short distances the soil profile description
presented in this report may not be representative of the entire soil system of the SCM footprint.
This report is provided to assist in the application for the SCMs by providing the soil information.
The permitting agency must issue the final permit. Any concurrence with the findings in this report
would be made at that time.

CLIENT:  ACC ConstructionPROJECT:  SOF Large TEMFLOCATION:  Fort Bragg, Cumberland County, North CarolinaF&R PROJECT No:  66X‐0030DRAWN BY:  T.T. WalkerDATE:  April 2019SCALE: Not to scaleFIGURENo.:BORING LOCATION MAP2CHECKED BY: R. Sanders, P.E.FROEHLING & ROBERTSON, INC.310 Hubert StreetRaleigh, North Carolina 27603‐2302|USAT 919.828.3441 | F 919.828.5751www.fandr.comEngineering Stability Since 1881Approximate F&R Boring Location (2019)C-1C-6C-9C-8C-2C-12C-14C-16C-13C-7C-17C-3C-4C-5C-10C-11C-15Approximate F&R Boring Location (2016)Approximate Percolation Test Location (2016)
1901952002052102152202252302352402452504911242034127C‐191530252029C‐101489161810C‐114892516141119C‐2491010823111729198553C‐33910222327721C‐44891623181219C‐5111117243916137C‐6576121211C‐7287151916C‐881321353516C‐9SUBSURFACE PROFILEProfile Name: Figure No. 3Plot Based on ElevationElevation (feet)City/State: Fayetteville, NCProject: Large TEMFClient: ACC Construction CompanyFroehling & Robertson, Inc.Project No: 66X‐0030RELEV_LANDSCAPE_8.5X11  66X‐0030 BORING LOGS.GPJ  F&R.GDT  4/2/19
1.5
3.5
5.0
8.0
10.0
15.0
1‐2‐3
2‐3‐4
3‐2‐4
3‐6‐6
5‐5‐7
8‐5‐6
GROUNDWATER DATA:
0 Hr: Dry inside PVC
24 Hrs: Dry inside PVC
0.5
2.0
3.5
15.0
0.0
2.0
3.5
6.5
8.5
13.5
5
7
6
12
12
11
SURFICIAL ORGANIC SOILS
NATIVE SOILS: Loose, Tan, Moist, Silty Fine SAND
(SM) with Trace Roots
Loose, Orange, Wet, Silty Clayey Fine to Medium
SAND (SC) with Trace Roots
Loose to Medium Dense, Brown, Moist to Wet,
Clayey Silty Fine to Medium SAND (SM) with
Trace Fine Gravel (8.5'‐10.0')
Wet from 8.5'‐10.0'
Boring Terminated at 15 feet.
242.5
241.0
239.5
228.0
Elevation: 243 ±Drilling Method: 2.25" ID HSA
Hammer Type: Automatic
Froehling & Robertson, Inc.
City/State: Fayetteville, NC
Project: Large TEMF
Total Depth: 15.0'
Date Drilled: 3/11/19
Remarks* Sample
BlowsElevationDescription of Materials
(Classification)
Boring Location: See Boring Location Plan
BORING LOG
Boring: C‐7  (1 of 1)
Driller: F&R Renza
SampleDepth(feet)Depth
R
N‐Value(blows/ft)
*Number of blows required for a 140 lb hammer dropping 30" to drive 2" O.D., 1.375" I.D. sampler a total of 18 inches in three 6" increments.
The sum of the second and third increments of penetration is termed the standard penetration resistance, N‐Value.
Client: ACC Construction Company
Project No: 66X‐0030
BORING_LOG  66X‐0030 BORING LOGS.GPJ  F&R.GDT  4/12/19
22422622823023223423623824024224424624825025515271211B‐145613182511B‐2678814B‐34883537B‐422489B‐521081611B‐659134217B‐72772129B‐82693917B‐9SUBSURFACE PROFILEProfile Name: Figure No. 5Plot Based on ElevationElevation (feet)City/State: Fort Bragg, NCProject: SOF Civil AffairsClient: USACOEFroehling & Robertson, Inc.Project No: 66U‐0198RELEV_LANDSCAPE_8.5X11  66U‐0198 BORINGS.GPJ  F&R.GDT  4/12/19