20140843 Ver 1_More Info Letter_20150626

NCDENR
North Carolina Department of Environment and Natural Resources
Pat McCrory
Governor
June 26, 2015
Harmon Graham Properties, LLC
ATTN:John Harmon
PO Box 180
Waynesville, NC 28786
Subject: Request for Additional Information
Jule Noland Drive Phase II
Dear Mr. Harmon:
Donald R. van der Vaart
Secretary
DWR # 14 -0843
Haywood County
On May 14, 2015, the Division of Water Resources (Division) received a revised stormwater
plan. The Division has the following comments on each stormwater control measure (SCll
1. SCM for Drainage Area #1— Bioretention Basin 1
a. The stormwater will overflow the berm at larger storm events. The contour lines
around Bioretention cell #1 show the top of the bioretention cell walls at 2581'
elevation. Since the drawing of the emergency overflow structure on SW 2
shows the "emergency overflow elevation" at 2581', the stormwater level could
rise above the walls of the bioretention cell and overflow the berm, adjacent
parking area, and finished floor elevation (2581') of the adjacent building. The
structural integrity of the cell would be compromised and you could expect a
breach in the berm in the future.
b. There is no documentation on the K -sat rates of the media in the bioretention
cell nor the insitu soils beneath the added media. The " Bioretention Cell
Supplement" sheets for drainage area #1 indicates that the "Planting media soil"
and the "In -situ soil" soil conductivity tests show a soil permeability of 0.75 " /hr.
There was no documentation on the infiltration tests for the in -situ soils as is
specified in the "Required Item Checklist" for a bioretention cell
(http: / /portal.ncdenr.org /web /Ir /bmp- manual). It specifies that "A soils report
that is based upon an actual field investigation, soil borings, and infiltration
tests" is required. It also specifies that "County soils reports are not an
acceptable form of soils information ". Please provide soils testing data
supporting the in -situ K -Sat numbers included in the plan.
Division of Water Resources — 401 & Buffer Permitting Unit
1617 Mail Service Center, Raleigh, North Carolina 27699 -1617
Location: 512 N Salisbury St, Raleigh, North Carolina 27604
Phone .[phone] FAX [phone]
Internet. www.ncwaterquality.org
An Equal Opportunity r Affirmative Action Employer Made in part by recycled paper

Harmon Graham Properties, LLC
DWR# 14 -0843
Request for Additional Information
June 26, 2015
Page 2 of 6
c. The specified 0.75 " /hr K -sat rate for the proposed bioretention media does not
meet the criteria specified in the Stormwater BMP Manual (The Manual). The
Manual provides in the "Major Design Elements" for bioretention cells on page
12 -2 that "Media permeability of 1 -6 in /hr is required, 1 -2 in /hr is preferred ".
d. The Manual specifies that underdrains are needed for bioretention cells in soils
such as those found on this site at the 0.75 " /hr infiltration rate. Major design
element # 18 in chapter 12 of The Manual indicates that "An underdrain shall
typically be installed if in -situ soil drainage is less than 2 in /hr." This was added
because of the drainage problems experienced in areas with marginal soils.
Please add appropriately sized underdrains and associated clean -out pipes to
bioretention cell #1. If underdrains are provided, you will not need to provide a
soils report for the in -situ soil as specified above.
e. Parts of the plan indicate that sod will be used as the cover for the bioretention
cell and parts show that hardwood mulch will be used. Drawing SW 2, under
"Bioretention Notes ", indicates that the surface will be covered with "Fescue or
Bluegrass sod." However, those same Notes also provide that "only triple
shredded hardwood mulch" should be used. The "Bioretention Cross Section"
on that page indicates that there will be "2 -4 inches Hardwood Mulch" on the
surface of the bioretention cell. The Bioretention Cell Supplement shows "depth
of mulch" at 4 inches but also indicates a "Y" (yes) for the question "Is this a
grassed cell ?" If mulch and plants are the plan, a deeper media and plant
specifications will be required. Please clarify whether you intend to use a sod
cover or plants and mulch.
f. Some practices included in the design are not required in The Manual. On page
12 -2 of The Manual it states that "A vegetated filter strip is not required for
overflows, bypass flows, or discharges from a bioretention cell." Your plan
includes these on the overflow discharge from Bioretention Cell #1, which could
add unnecessary costs to your stormwater plan. If this was added to make up for
some deficiency in the bioretention cell design, please let us know.
2. SCM for Drainage Area #2 - Extended Dry Detention Basin 2
a. The basin is undersized to treat the design storm and the calculations are not
correct. From the engineering drawings provided for basin #2, there is not
enough storage to meet the applicant's calculated "Minimum required volume ".
The applicant's Supplement states that 3779 cu. ft. is the "Minimum required
volume." However, on that sheet, the applicant indicates that the "volume
provided" is 5279.00 cu.ft. This number is incorrect and the actual "volume
provided" is probably near the 2007 cu. ft. stated as "Incremental Volume" on
the "Stage Storage Volume Calculation Table." This is insufficient to detain the
design storm volume of 3779 cu.ft.

Harmon Graham Properties, LLC
DWR# 14 -0843
Request for Additional Information
June 26, 2015
Page 3 of 6
The Manual shows in Figure 17 -4 that the Temporary Pool Volume (or water
quality volume) is measured from the "Sediment Removal Elevation" to the
"Temporary Pool Elevation." The available temporary (or water quality) storage
should be calculated from the elevation of the orifice at 2579' up to the
elevation of the emergency overflow at 2580. There is only one foot of storage
available, not two as it indicated in the plan.
As shown in the BMP Manual (page 17 -2), one foot of freeboard must be
provided above the emergency overflow. The applicant's "Stage Storage Volume
Calculation Table" on sheet SW 3 shows the one foot of freeboard as being
"over 2581" feet elevation. That would seem to indicate that the foot of
freeboard is provided above the top of the 2581' elevation of the berm when
actually the one foot of freeboard is provided above the emergency overflow at
2580'. However, as shown above, if the orifice is at 2579' and the emergency
overflow is at 2580', then there is only one foot of storage, not two.
b. Please provide more details on the pipe to the energy dissipater. Please provide
elevation details on the 24" culvert that leads to the energy outlet along with
elevations on the dissipater.
3. SCM for Drainage Area #3 - Extended Dry Detention Basin 3
The basin is undersized to treat the design storm and the calculations are not
correct. From the engineering drawings provided for basin #3, there is not
enough storage to meet the applicant's calculated "Minimum required volume ".
The applicant's Supplement states that 2737 cu. ft. is the "Minimum required
volume." However, on that sheet, the applicant indicates that the "volume
provided" is 5108.00 cu.ft. This number is incorrect and the actual "volume
provided" is probably near the 1806 cu. ft. stated as "Incremental Volume" on
the "Stage Storage Volume Calculation Table." This is insufficient to detain the
design storm volume of 2737 cu.ft.
As explained in #2 above, the storage should be calculated from the elevation of
the orifice at 2579' up to the elevation of the emergency overflow at 2580'.
There is only one foot of storage available, not two as it indicated in the plan.
Also as stated in #2 above, the one foot of freeboard must be provided above
the emergency overflow. The applicant's "Stage Storage Volume Calculation
Table" on sheet SW 3 shows the one foot of freeboard as being "over 2581" feet
elevation. Again, that would seem to indicate that the foot of freeboard is
provided above the top of the 2581' elevation of the berm when actually the one
foot of freeboard is provided above the emergency overflow at 2580'

Harmon Graham Properties, LLC
DWR# 14 -0843
Request for Additional Information
June 26, 2015
Page 4 of 6
4. SCM for Drainage Area #4 — Stormwater Bioretention 4
a. There is no documentation on the K -sat rates of the media in the bioretention
cell nor the insitu soils beneath the added media. The "Bioretention Cell
Supplement" sheets for drainage area #4 indicates that the "Planting media soil"
and the "In -situ soil" soil conductivity tests show a soil permeability of 0.75 " /hr.
As discussed in #1 above, there was no documentation on the infiltration tests
for the in -situ soils as is specified in the "Required Item Checklist" for a
bioretention cell.
b. The specified 0.75 " /hr K -sat rate for the proposed bioretention media does not
meet the criteria specified in the The Manual. As discussed in #1 above, The
Manual provides in the "Major Design Elements" for bioretention cells on page
12 -2 that "Media permeability of 1 -6 in /hr is required, 1 -2 in /hr is preferred ".
c. The Manual_ specifies that underdrains are needed for bioretention cells in soils
such as those found on this site at the 0.75 " /hr infiltration rate. Major design
element #18 in Chapter 12 of The Manual indicates that "An underdrain shall
typically be installed if in -situ soil drainage is less than 2 in /hr." Please add
appropriately sized underdrains and associated clean -out pipes to bioretention
cell #4. If underdrains are provided, you will not need to provide a soils report
for the in -situ soil as specified above.
d. Parts of the plan indicate that sod will be used as the cover for the bioretention
cell and parts show that hardwood mulch will be used. As in #1 above, Drawing
SW 2, under "Bioretention Notes ", indicates that the surface would be covered
with "Fescue or Bluegrass sod." However, those same Notes also provide that
"only triple shredded hardwood mulch" should be used. The "Bioretention Cross
Section" on that page indicates that there will be "2 -4 inches Hardwood Mulch"
on the surface of the bioretention cell. The Bioretention Cell Supplement shows
"depth of mulch" at 4 inches but also indicates a "Y" (yes) for the question "Is
this a grassed cell ?" If mulch and plants are the plan, a deeper media and plant
specifications will be required. Please clarify whether you intend to use a sod
cover or plants and mulch.
e. Some practices included in the design are not required in The Manual. On page
12 -2 of The Manual it states that "A vegetated filter strip is not required for
overflows, bypass flows, or discharges from a bioretention cell." Your plan
includes these on the overflow discharge from Bioretention Cell #4, which could
add unnecessary costs to your stormwater plan. If this was added to make up
for some deficiency in the bioretention cell design, please let us know.
f. Can't determine the destination for stormwater discharge from Bioretention cell
#4. On that portion of the plan, there is a "Bypass weir" designed for emergency
overflow as is shown on SW 3. The drawing does not provide adequate detail,
such as its location or elevation, to enable us to determine how and where the

Harmon Graham Properties, LLC
DWR# 14 -0843
Request for Additional Information
June 26, 2015
Page 5 of 6
stormwater, high -flow bypass will leave the bioretention cell. Furthermore, it is
not at all clear how the stormwater will leave the filter strip and travel off the
site. Please revise the drawings to make it clear where stormwater flows from
the cell #4 area and eventually leaves the site. There appears to be a ditch
flowing in an east -west direction on the south side of drainage area #4 but it is
not clear where it goes. There are no elevation points to enable us to determine
if the stormwater will travel by gravity across the site to its discharge point on
the west side or does it exit the site on the east side? There seems to be a ditch
along the southwest corner of drainage area #4. Is that ditch part of the
stormwater discharge system? Without those specifications on the plan, the
channels may not be installed correctly.
g. We are unable to document the actual storage capacity of #4 bioretention basin.
The Stage Storage Volume Calculation Table shows a cumulative storage volume
of 8980 cu. ft. at the 2583' elevation. We know this is significantly over the
actual storage capacity. If the bypass weir is in a part of the dam as the "Cross
Section Bypass Weir" drawing indicates, then storage at 2583' elevation is not
possible. We see from the drawing that there is a V -weir shaped rock weir
where emergency flow exits and which must be lower than the 2583' elevation.
As we see it, the collected stormwater will flow through the stone structure and
much of it will bypass the intended infiltration into the bioretention cell.
Because there are no elevations on the drawings regarding the weir, it is difficult
to document what will happen. However, with a pervious, stone weir that
seems to be 4 -5' in depth, we know that the stormwater will not be stored at
2583' as is shown on the plan. It will flow to the base of the rock structure and
not be infiltrated as was intended. Please explain the intent of that design.
5. Miscellaneous Issues
a. The "General Notes' on plan sheet SW 1 state that cores taken by Altamont
Environmental in drainage areas #2 and #3 show SHWT elevations at 2574.5' and
2575'. We could not find those references in the February 14, 2014 report.
Please indicate which page(s) in the report this information can be found.
b. Please check all of the dimensions and volumes of the four basins. It is possible
that the drawings are a little off - scale. We only checked basin #4 and according
to the drawing, the surface of the top of the cell seems to be about 4,500 sf not
the 5,390 sf as was entered into the Supplement.
c. As is specified in the "Required Items Checklist ", please provide the calculations
for the Orifice Outlet Drawdown Time as presented in SW 3. What is the K rate
provided and how was it used in the calculations?

Harmon Graham Properties, LLC
DWR# 14 -0843
Request for Additional Information
June 26, 2015
Page 6 of 6
d. It is not clear which "basin" the "Basin Cross Section Detail" on SW 2 applies to
or the "Outlet Detail" on that same page. Are they both meant to apply to the
extended dry detention basins? Both drawings have a 15" outlet culvert which is
only specified for the Bioretention Basin.
Please contact Boyd DeVane at 919 - 807 -6373 or boyd.devane @ncdenr.gov if you have any
questions or concerns.
Sincerely,
I <
,Oj „
Karen Higgins, Supervisor
401 & Buffer Permitting Unit
cc: Wanda Austin, Wanda H. Austin, PE Engineering (via email)
Russell L. McLean, III, McLean Law Firm, P.A. (via email)
Burton Edwards (via email)
John Payne, NC Attorney General's Office (via email)
DWR ARO 401 file
DWR 401 & Buffer Permitting Unit file
Filename: 140843JuleNolandDrPh I I(Haywood)_SW_HOLD