SW1080104_Calculations_20080507

vMCKIN4&CREED
rE/ r
t 4
1� M AY - 7 2008
,4
WATER COfd 1T`.' H(,7101 �
Mills River Elementary School
MC # 4099-0007
CALCULATIONS FOR:
Erosion Control
Water Quality
DATE. 12/17/07
p s10 y =
REV. 02/18/08 �'.QQ°
5E t
75 S •
0
8020 TOWER POINT DRIVE. CHARLOTTE, NORTH CAROLINA 28277
TEL [phone] FAX [phone] www.mckimcreed.com

rte Description
he new Mills River Elementary School is located at the southwest corner of the intersection of School House Road (SR 1426) and
Banner Farm Road (SR 1331). Beside the current location of the existing Mills River Elementary School. The project will disturbed
approximately 8.36 acres. The existing conditions for the new school site is primarily a grassed field. The development will consist of
n elementary school, associated parking, and storm drainage facilities.
Hydrology
the is a new wet detention basin was design to handling the total drainage for the new school site. The new wet detention basin will be
Gated on the south side of the proposed site long the north side of the existing creek.
Summary
Ihe NCDENR Stormwater BMP Manual was used to design the new wet detention basin. The wet detention basin meets all design
ritiera outline in the NCDENR Stormwater BMP Manual. (See the Water Quality Basin Calculations.)
&RAINAGE AREAS:
(see attached drainage area map)
It! nTF-1
Predevelo
ed Drainage Area =
11.5
acres
0.017969
s . miles
Postdevelo ed Drainage Area= 11.5 acres
0.017969
s . miles
1
0
0
I
1 Page 1 of 1

1
Mills River Elementary School
V
SEDIMENT BASIN CALCULATIONS
PROJECT NO 4099-0007
BY: mdb
DATE: 12/17/07
REVISED:
T.M.: mdb
P.M.: bjd
RISER TYPE BASIN DESIGN FOR SEDIMENT BASIN #1
I
DRAINAGE AREAS/REQ'D STORAGE
DESIGN CRITERIA
Total drainage area TDA 11.50 ac
Pro osed sediment depth 2 ft
Disturbed area DA 8.36 ac
Bottom elevation of basin 2102 msl
Required sediment storage( 1800xTDA 20700 cf
Depth of flow over spillway 1 ft
BASIN CONFIGURATION
Bottom elevation
2102 msI
Sediment Storage elevation
2104 msl
Spillway crest
2104 msl
Top of Berm
2106 msl
ESTIMATED BASIN SIZE RECTANGULAR
Length(ft) Width(ft)
Bottom 140 68
Top 156 84
BASIN EFFICIENCY
Sediment storage provided: 30117 OKAY
Sediment storage required: 20700 cf
Surface area/Flow comparison: 16112 OKAY
DESIGN FLOW 1
Bare soil coefficient 'C' =
Com osite 'C'=
Area 'A' =
10 yr. storm rainfall intensity, T =
Computed flow from site. 'O' =
.ANNED BASIN SIZE
EFER TO EROSION CONTROL PLAN
Elev. Area (SF) Cumulative Volume
2102
14022
0
2103
15050
14536
2104
16112
30117
2105
17209
46778
2106
18341
64553
X
X
######
X
X
######
X
X
######
X
X
######
X
X
######
X
X
######
X
X
######
11 RISER/EMERGENCY SPILLWAY DESIGN
0.6 Riser pipe diameter X in
0.4
11.5 ac Depth of flow 1 ft
7.03 in/hr
32 cfs lFlow through riser: #VALUE! cfs #VALUE!
OUTLET PIPE DESIGN
Outlet pipe diameter
X #VALUE!
Flow through outlet pipe #VALUE! cfs
(Note: Flow determined using outlet controi and pipe 80% full)
OUTLET PIPE IS #VALUE!
Pipe slope (ft/ft)
X Rift
Pipe length(ft)
X ft
1
Outlet pipe invert in
2102
'Outlet pipe invert out
#VALUE+
CONCRETE ANCHOR SIZE
Length of exposed outlet pipe X ft Safety factor 1.2
Buoyancy = #VALUE! lbs
Anchor width
X
ft
Required Volume of Anchor = #VALUE+ cf
Anchor Length
X
ft
Actual Volume of Anchor= #VALUE! cf
Anchor Thickness
ix
ft
#VALUE!
1
PERFORATION S
1
Required Area of Holes = (As*(2*h)A.5)/(T*Cd*20428)
t #VALUE! sf
Proposed hole dia= 0.5 in
# of holes re uired= #VALUE!
As = Surface Area of Basin =
16112 sf
h = Maximum head of water =
2 ft
T = Time to discharge Water =
10 hrs
Cd = 0.6
SURFACE AREA/FLOW COMPARISON:
Formula:
A=0.01 *Q
1
7.03 10 year storm
A:
Minimum Surface Area (acres) measured
at the crest of the principal spillway
design):
32 CFS
A(Required) :
13939 sf of surface area at sed stor elev
.
O:
Peak inflow rate of 10 year storm in cts
A Provided
16112 OKAY
E
Page 1 of 1

Mills River Elementary School
PROJECT NO.: 4099-0007
BY: mdb
MCIGM
DATE: 12117107
T.M.: mdb
REVISED: 01121108
P.M.: bid
WATER QUALITY BASIN CALCULATIONS
WATER QUALITY REQUIREMENTS
To meet the Water Quality requirements, the procedure outlined in the "Stormwater Best
Management Practices" published by NCDENR will be used. This guide gives the
required pond surface area and storage volume to meet an 85% pollutant removal
efficiency. Also, the pond must detain the first 1 " of rainfall and release this volume
over a period of 2 to 5 days. Calculations for these requirements are as follows:
Surface area requirements
Drainage area to pond (Da)= 11.5 Ac
Post -development impervious percentage = 45%
Average pool depth = 4 ft
Designed permanent pool elevation = 2102
From table 1.1 in the BMP guidelines the required Surface Area to Drainage Area
Ratio (SA/DA) for a permanent pool depth of 4 feet = 1.73
Required surface area = SA/DA1100 x Drainage area= 0.20 Ac
Surface area of pond as designed at permanent pool elevation = 0.21 Ac
1 " rainfall requirements
Using the runoff volume calculations in the "Simple Method"
Rv = 0.05 + .009 (1)
Rv= 0.455 in/in
Volume = (Design rainfall) (Rv) (Drainage Area)
Volume = 1 " rainfall x Rv in/in x 1/12 in/ft x Da = 0.44 ac-ft
or 18994 ft^3
This volume must be released over a period of 2-5 days
% PERMANENT POOL DEPTH
Impervious 3 4 5 6 7 8 9
10
0.59
0.49
0.43
0.35
0.31
0.29
0.26
20
0.97
0.79
0.7
0.59
0.51
0.46
0.44
30
1.34
1.08
0.97
0.83
0.7
0.64
0.62
40
1.73
1.43
1.25
1.05
0.9
0.82
0.77
50
2.06
1.73
1.5
1.3
1.09
1
0.92
60
2.4
2.03
1.71
1.51
1.29
1.18
1.1
70
2.88
2.4
2.07
1.79
1.54
1.35
1.26
72
2.98
2.48
2.13
1.85
1.6
1.4
1.35
80
3.36
2.78
2.38
2.1
1.86
1.6
1.42
85
3.55
2.94
2.52
2.22
1.99
1.72
1.55
90
3.74
3.1
2.66
2.34
2.11
1 1.83
1.67
® M ® ® ® M M ® ® = ® M ® = M M ® M

As designed pond areas:
Storage Volumes
Cumulative
Elevation
Area(ac)
Volume(ac-ft)
2102
0.2054
0.00
2102.5
0.2582
0.12
2103
0.2741
0.25
2104
0.3072
0.54
2105
0.3421
0.86
2106
0.3788
1.22
Interpolation to find elevation at which required storage volume is reached
Storage Storage
Elev volume area
2103 0.25 0.27
Elev 0.44 0.30
2104 0.54 0.31
Elev= 2103.65
Storage elevation = 1.65 feet above permanent pool elevation
Determination of Orifice size for 2-5 day drawdown
Q = Cd'A` 2'g'Ho
Assumed orifice 2"
A = Area of orifice A = .021 ft^2
Cd = Coefficient of discharge Cd = 0.6
g = Acceleration of gravity g = 32.2 ftls^2
Ho = Driving Head Ho = 0.98
Q=0.10cfs
Orifice Size = 2"
Assumed Q to be 0.11 cfs
The Q flowing through the orifice must be lower than 0.11 cfs
Permanent Pond Storage Volume
Elevation
(ms!)
Area
(SO
Area
(ac)
Volume
(cu-ft)
Volume
(ac-ft)
2092
1 100
0.0023
0
0.0000
2093
282
0.0065
183
0.0042
2094
619
0.0142
622
0.0143
2095
882
0.0202
1368
0.0314
2096
1316
0.0302
2459
0.0564
2097
1982
0.0455
4095
0.0940
2098
2799
0.0643
6471
0.1486
2099
3767
0.0865
9739
0.2236
2100
4885
0.1121
14049
0.3225
2101
6153
0.1413
19550
0.4488
2101.5
6845
0A571
22795
0.5233
2102
8946
0.2054
26727
0.6136
2102.5
11248
0.2582
31759
0.7291
2103
11940
0.2741
37550
0.8620
2104
13382
0.3072
E 50191
1.1522
2105
14903
0.3421
64313
1.4764
Average Pool Depth = 2.9876
® ® M M M iiiiiiis M iiiiiis ® M M M M ® ® M ® ® M

1 year 24 hour storm volume mitigation for difference between pre and post conditions
Q= P-2S ^2
As designed pond areas:
(P+.8S)
Storage Volumes
S= 1000 -10
Cumulative
CN
Elevation Area(ac) Volume(ac-ft)
2102 0.2054 0.00
P= rainfall(in) - 1 year 24 hour storm
2.3 in
2102.5 0.2582 0.12
CNpre= SCS curve number
83
2103 0.2741 0.25
Qpre= computed runoff
0.91 in
2104 0.3072 0.54
CNpost= SCS curve number
91
2105 0.3421 0.86
Qpost= computed runoff
1.43 in
2106 0.3788 1.22
Qdif= Depth of increased runoff
0.52 in
0 0 0.00
DA= Drainage area
11.5 ac
V= 1 year runoff volume (DAxQ)
21804 ft^3
0.50 ac-ft
Interpolation to find elevation at which required storage volume is reached
Storage Storage
Elev volume area
2103 0.25
0.27
Elev 0.50
0.30
2104 0.54
0.31
Elev= 2103.87
Storage elevation =
1.87 feet above permanent pool elevation
Water quality pond draw down rate (cfs)
Required Volume(ft^3) / Draw Down Time(s) = 0.10 cfs
Level Spreader Length
Draw Down rate x 13ft= 13ft
Minimal 13 ft
CONCLUSION: WATER QUALITY REQUIREMENTS ARE MORE RESTRICTIVE THAN 1 YEAR 24 HOUR
AND WILL GOVERN BASIN DESIGN PARAMETERS
M ®® M® M M®® M® M® ® M =1 M M M

1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Mills River Elementary School •
v
PROJECT NO. 4099-0007 BY: mdb
DATE: 12/17/07 T.M.: mdb
REVISED: 02118108 P.M.: b"d RIPRAP APRON DESIGN
25
20
� ?5
C
yo 10
5
fl 5 10 15 20 25
Do in feet
TO PREVENT SCOUR HOLE
I RIPRAP
CLASS
ZONE
APRON MATERIAL
STONE DIAMETER
LENGTH OF APRON
DEPTH
1
Stone Filling (Fine)
6"
4 x (pipe diameter)
10"
!
2
Stone Filling (Light)
6"
6 x (pipe diameter)
12"
1
3
Stone Filling (Medium)
13
8 x (pipe diameter)
18"
11
4
Stone Filling (Heavy)
23"
8 x (pipe diameter)
30"
H
5
Stone Fillip (Heavy)
23'
10 x (pipe diameter)
30"
11
6
Stone Fillip (Heavy)
23'
12 x (pipe diameter)
30"
It
7
Special Study Required (Ener y Dissipators, Stilling Basins, or Larger Sue Stone
Apron wtarn = pipe aramerer + u.4-(apron tengrn) vet= (u.3uu-(atam)^y3"(Stope)^712JIn
FES #
DIA
(ft)
SLOPE
(ft/ft)
n
I V
(ftls)
ZONE
RIP RAP
CLASS
LENGTH
(ft)
I WIDTH
(ft)
I DEPTH
(in)
1
4
0.005
0.013
11.73
3
II
32
17
18
xxx
xx
xxxx
XXXX
######
xx
#VALUE!
#VALUE!
XXX
xx
XXXX
XXXX
######
xx
#VALUE!
#VALUE!
XXX
xx
XXXX
XXXX
######
xx
#VALUE!
#VALUE!
XXX
xx
XXXX
XXXX
######
xx
#VALUE!
#VALUE!
XXX
xx
XXXX
XXXX
######
xx
#VALUE!
#VALUE!
XXX
xx
XXXX
XXXX
######
xx
#VALUE!
#VALUE!
XXX
xx
XXXX
XXXX
######
xx
#VALUE!
#VALUE!
XXX
xx
XXXX
XXXX
######
xx
#VALUE!
#VALUE!
XXX
xx
XXXX
xxxx
######
xx
#VALUE!
#VALUE!
XXX
xx
XXXX
XXXX
######
xx
#VALUE!
#VALUE!
xxx
xx
XXXX
XXXX
######
xx
#VALUE!
#VALUE!
Source: "LianK ana cunannel Lining Hroceoures", New York Uepartment of I ransportatlon,
Division of Design and Construction, 1971.
Page 1 of 1

0--i
--,
0 o
Ditch No.
III►►►
o
a
t
n
Contributing Area
n
0
ri
N
m
"
(Acres)
i
m
—
Z
0
0
o
n
Runoff Coefficient
�
yI ;U
Rainfall Intensity
n
r-
Wo
Wo
Wo
(in/hr)
m
0m
—WmN
y
n
C,
o
r
Length (ft)
G�i
0
0
0
0
_
m
r
0
0
0
°
Depth (ft)
14
D
—
_
I
o
o
rr
Bottom width (ft)
n
D
0
o
Z
^za,Z
0
0
o
top width (ft)
D
M
r
Side Slopes
n
(xH:1V)
❑
--
3
Mannings No. (n)
C
ham,
0
M
Full Capacity (cfs)
w
~
�
❑
Z
Design Flow (cfs)
U]
PO
Design Flow
m
ni
C
Depth (ft)
o
41
a
rn
N
"'
Design Flow
Velocity (fps)
0
0
0
slope of Ditch
W
N
(off)
A
Shear Stress
n
U
(Psf)
m
g)
gn
�w
f
w
f
p1
Er
Er
Channel Lining
N
m
m
m
Type
m
a
ITT]
I
I
I
1
11
1
1
1
11
1
1
1
1
1
1 t
t
`
Acceptable
n
1
I
I
I
I
1

1 31 December 2007
I
'4 iWr� 1
MAY - 7 2008 `
vJ rr 0 �r,..;T - "c �cN
p ..HrVll LE
Mr. Chad Heatherly via Hand Delivery
Henderson County Public Schools
414 Fourth Avenue West
Hendersonville, NC 28739-4261
' f oil H Properties
Subject: Sods Investigation and Assessment o S Hydraulic opert
Affecting Proposed Stormwater Infiltration and Retention Facilities
Mills River Elementary School
Horse Shoe, Henderson County, North Carolina
Dear Mr. Heatherly:
This letter report presents the results of a soils investigation of soil hydraulic properties relevant
to proposed stormwater infiltration and retention facilities, to serve a proposed new elementary
school. Soil interpretations relevant to design and permitting of the proposed facilities are also
provided.
1 The proposed new elementary school is proposed to be located at the site of the present Mills
River Elementary School (MR -ES), on School House Road, in Horse Shoe, Henderson County.
This work was performed by David L. Hargett, Ph.D., CPSS, CPSC, CGWP, a Licensed Soil
Scientist (NC LSS # 1139), through his firm Hargett Resources, Inc. (HRI).
1 Background
1 HRI was retained by Henderson County Public Schools (HCPS), to provide technical assistance
with respect to soil conditions that could affect the viability of proposed stormwater infiltration
facilities (bioswales or the like) and stormwater retention facilities at the MRES site.
Accordingly this investigation focused on three specific areas of the site identified by McKim &
Creed of Charlotte, NC, the design engineering firm for the proposed new school. A particular
issue of interest with respect to the stormwater facilities is the suitability of site soils for the
proposed stormwater facilities as considered by LEED design standards. The objective of this
consultation was to assess limiting soil hydrologic conditions and advise HCPS on site and soil
conditions as they may affect design, placement, construction, and performance of the proposed
stormwater features.
p. r of
Hargett Resources, Inc., 408 Deepwood Drive, Greer, SC 29651
Plrotie 86d.787.816t1 dhcrrgett-5?CDi?gnutil.cottr
4

Henderson County Public Schools., Soils Investigation —Mills River Elementary School, 31 December 2007, p. 2 of 6
L�
0
I
11
1
1
Note that the primary intent of this investigation was to assess the suitability of soil conditions
for the proposed stormwater facilities. The scope of this effort did not include design
calculations, layout, or specifications. Interpretations of soil conditions are offered in this report
with regard to general soil suitabilities, but specific input to the design of facilities is not within
the scope of the present study, and HRI does not accept any responsibility for facility design.
General Site Conditions
This tract is located within the Blue Ridge Physiographic Province. The rocks of this area of the
Mountains region are generally comprised of felsic metamorphic and igneous materials
(dominantly mica schist, gneiss, granite gneiss, mica gneiss, granodiorite and granite) (Natural
Resources Conservation Service, Soil Survey of Henderson County, North Carolina, 1980 and
2007).
HCPS, through its design engineer, McKim & Creed, identified three areas on the HES property
for evaluation. These areas are identified in Figure 1 by the symbol "X". All areas examined
were in or adjacent to an grove of large hardwoods, and a playground. Areas 1, 2, and 4 were
determined to represent a relatively undisturbed topography and intact natural soil profiles
subject to little disturbance other than historic logging, agricultural, and landscaping activities.
Area 3, adjacent to a built up area at the rear entrance to the school, has clearly been subjected to
grading and filling at the time of construction of the present school complex, and thus the soils
are a mix of fill and natural materials.
The dominant soil series mapped on these upland landscape positions in this area of Henderson
County is the Fannin series and associated series and mapping units (MRCS, Soil Survey of
Henderson County, Web Soil Survey, 2007), as shown in Figure 2. Soils in the Fannin series are
very deep, well -drained, and have moderate permeability. These soils formed in material
weathered from metamorphosed rocks, high in mica content, predominantly mica schists and
mica gneisses. These soils typically have loam surface horizons, grading to subsoils of clay
loam texture. The subsoils grade to disintegrated saprolite, or weathered schists and gneisses,
with loamy texture. Bedrock generally exists at depths greater than six feet, or more.
Supplemental information on the Hayesville and Tate soils is appended to Figure 2 for reference.
Information on the Fannin series is appended to Figure 2. While these soils may fairly represent
conditions on other portions of the MRES site, the soil conditions investigated on this portion of
the site were not consistent with the range of characteristics of the Fannin series.
Investigative_ Procedures
HRI conducted its field investigations and soil characterization activities at the NIRES site on 1 I
and 12 December 2007. The scope of this investigation involved examination of backhoe
excavated test pits, hand borings, bedrock probes, and determination of saturated hydraulic
conductivity (Ksat) for selected representative soil strata. Test pits were installed and inspected
on the first day, and Ksat tests were conducted on the second day. Test Pits were installed by
Hargett Resources, Inc., 408 Deepwood Drive, Greer, SC 29651
Phone&4.787.8160 c!lxr,geu53�gnur!l.carr

Henderson County Public Schools., Soils Investigation — Mills River Elementary School, 31 December 2007, p. 3 of 6
I
King Excavating of Hendersonville. Weather conditions on I 1 December were unseasonably
warm, — 65' F and clear. Conditions on 12 December were not as warm, — 60' F, and overcast.
Area 1: This topographically lowest portion of the site, near an ephemeral drainage ditch, is
shown in Figure 1. This area projected to have a stormwater retention basin. Soils underlying
this feature should ideally have slowly permeable subsoils and substratum and the potential to be
compacted to provide low permeability conditions. Test Pit # I was installed in this area roughly
20-30 feet west of the target "X" location (per Fig. 1). A hydraulic conductivity test was
subsequently conducted in the center of this area as shown on Figure 1. Photographs of all test
pits and the locations of various investigation activities are provided in Figure 3 (A-F).
Area 2: Area 2 is located between TP #1 and the center target "X" location. This area represents
soil conditions potentially applicable to the northernmost two target locations. This center target
location is anticipated to have a stormwater bioswale in this area. Soils underlying this feature
should ideally have moderately permeable subsoils and substratum to enable gradual infiltration
of stormwater temporarily detained in the swale. Test pit #2 was installed in this area as shown in
Figure 1. This test pit location is roughly 4 ft higher in elevation than TP #l. A hydraulic
conductivity test was subsequently conducted adjacent to this test pit.
Area 3: Area 3, as shown in Figure 1 is in the southeastern corner of the existing school site,
immediately adjacent to the rear entrance road to the school, and just adjacent to a freestanding
storage building. This area has clearly been filled, and is immediately adjacent to a drainage
ditch at the rear property line. Test Pit #3 was located in this area as shown in Figure 1. Because
soil conditions were confirmed to be fill to a depth of several feet, and because of the steep slope
break to the drainage ditch, no hydraulic test was conducted at this location.
Area 4: This area is in the area of the existing swale draining the existing school building, as
shown in Figure 1. Test Pit #4 was installed in this area. A hydraulic conductivity test was also
conducted adjacent to this test location.
Results of Soils Investigation
Soil conditions in Areas 1, 2, and 4 were relatively consistent. A detailed soil profile description for a
representative test pit (TP #1) is provided as Table 1. Summaries of soil conditions observed in all
four test pits are provided in Table 2. Photographs of all test pits are provided in Figure 3 (A F). The
soils observed are generally more poorly drained than the Fannin series mapped by MRCS in this area.
The soils observed in TPs #1, 2, and 4 generally presented loamy surface horizons, with subsoils of
silt loam to clay loam texture. In the context of the Unified Soil Classification System these entire
profiles typically are silty sands (S" to sandy silts (MIL) with some strata of silty clay (CL). The
subsoil horizons were typically firm at depths of roughly 15 to 30 inches below grade. The
substratum becomes very firm and massive with depth. These soil profiles reflected extremely deep
weathering zones and did not have any significant rock or parent material apparent within the test
Hargett Resources, Inc., 408 Deepwood Drive, Greer, SC 29651
Phone [phone] dlrabe!!,52�r gmetil.com
I

1 Henderson County Public Schools., Soils Investigation— Mills River Elementary School, 31 December 2007, p. 4 of 6
pits. Test pits were generally terminated at 70-78 inches below grade. Bedrock probes in the test pits
revealed no refusal to depths of 10 to 12.5 ft below grade in any of the test pits.
The soil profiles for TP #1, 2, and 4 reflected very significant mottling and gleying at shallow depths
suggesting likely seasonal saturation at depths of roughly 36 inches. These conditions may be
indicative of true seasonal saturation, a perched groundwater zone, or such slow permeability that
internal drainage is significantly impaired. Note that at the time of this site investigation the region
had experienced unprecedented drought, with annual precipitation approximately 35 percent below
normal locally for calendar year 2007.
TP #4 confirmed approximately 40 inches of mixed fill material above what appeared to be an
original topsoil horizon. The natural profile below that depth appeared to have natural morphologic
characteristics. Given the location of this pit, the presence of fill, the steep adjacent slope, and the
close proximity to the property line, no further testing in this area was believed to be warranted.
In the geotechnical investigation for the proposed school building construction area no groundwater
(perched or otherwise) was observed in any of the hollow -stem borings installed on the adjacent
playing fields area_ (Bunnell-Lammons Engineering, Inc., Report of Preliminary Geotechnical
Exploration, Mills River Elementary School, on behalf of HCPS, 8 September 2006). None of these
borings were in the immediate area assessed in the present soils investigation. The geotechnical logs
did all confirm very consistent deep silty soil profiles to depths of roughly 20 ft.
1 Soil Hydraulic Conductivity Properties
A key objective of this investigation was to determine saturated hydraulic conductivity (Ksat) values
for representative soil horizons that could affect the placement and design of the proposed stormwater
infiltration and retention facilities. Ksat was measured by using a modified constant head
permeameter adapted to measurement of conductivity in specific strata in a borehole. The method and
device employed here is similar to the "Guelph Permeameter" method of Reynolds et al. (W D.
Reynolds, D.E. Elrick, and B.E. Clothier, 1985. The constant head well permeameter. Soil
Science. 139:172-I80). Hydraulic conductivity was solved using the method of Glover (A.
Amoozegar, 1989. Comparison of the Glover solution with the simultaneous -equations
approach far measuring hydraulic conductivity. Soil Sci. Soc. Am. J. 53:1362-1367).
In addition, one undisturbed "pedestal" (cylindrical mass) of substratum soils was evaluated in
the laboratory for Ksat according to a method modified from the "Crust Test" of Bouma et al. (J.
Bouma, C Belmans, L. W. Dekker and W.JM. Jeurissen 1983. Assessing the suitability of soils
with macropores for subsurface liquid waste disposal. J. Environ. Qual. 12: 305-311). In this
case the undisturbed "pedestal", roughly 4 in. diameter by 8 in. length, was carefully carved from
the desired substratum depth, and coated with hydraulic cement for transport to the laboratory.
The sample was subsequently prepared in the lab for Ksat measurement using a constant head
arrangement, per the method of Bouma.
The results of the Ksat tests at the MRES site are presented in Table 3. The three field tests
performed at the various locations and strata selected for assessment produced consistent values
Hargett Resources, Inc., 408 Deepwood Drive, Greer, SC 29651
Phone [phone] dliar-el152 a onrarl.cam

1
Henderson County Public Schools., Soils Investigation — Mills River Elementary School, 31 December 20OZ p. 5 of 6
J
0
I
0
I
1
I
0
I,.'
0
1
of 1.60, 6.40, and 432 cm/day. This last value is believed to be an anomaly and attributable to a
possible root channel or worm channel, which were observed in some locations in the test pits.
For this reason the author recommends disregarding this higher value. The range of 1.60 to 6.40
cm/day is roughly equivalent in lay terms to approximately 4.4 to 18 inches per week.
The laboratory Ksat measurement for the pedestal taken from TP #1 produced a somewhat lower
value, 0.92 cm/day. It is the opinion of the author that these three lower values are good and
representative values for Ksat for the soils evaluated and consistent with expected values based
on observations of soil morphological features in the test pits at the site.
Note that with the equipment available and given considerations of safety and practicality for the
given scope of work, testing of zones deeper than approximately 52 inches was not practicable.
Regardless, it is the author's opinion based on observations of soil morphology from the test pits
excavated to depths as great as 78 inches, that the zone between 4-8 ft depth would have Ksat
values consistent with the lower range measured for the shallower depths (2-10 cm/day). Note
that due to the inherent variability of soil physical properties, soil morphology, the potential
presence of macropores, root channels and other features, soil Ksat values can vary dramatically
within similar soil materials and in depth -specific strata even over a distance of a few feet.
Interpretations with Respect to Stormwater Infiltration and Retention Facilities
For the soils observed in this investigation profile permeability characteristics are expected to be
very limited for the function of bioswales where the objective is to detain and gradually infiltrate
moderate quantities of runoff from nearby impervious surfaces. The subsoil and substratum Ksat
values are expected to be limiting to the amount and rate of infiltration. Based on the
observations of soil conditions from the test pits, and inferring from the boring logs from the
nearby geotechnical investigation, more permeable strata is not expected within a reasonable
depth. Therefore, these conditions would not likely, be overcome by the incorporation of a
vertical trench of more permeable media to enhance vertical infiltration. Subsurface French
drains to some perimeter discharge point may be feasible but may not meet the design objectives
of infiltration bioswales.
For purposes of constructing retention / detention ponds capable of holding stormwater for
treatment and gradual release, the site substratum soils are expected to be well adapted. The
construction of the pond lining and sideslopes would benefit from some degree of compaction by
appropriate heavy equipment to generally reduce permeabilities further and render infiltration
conditions more consistent across the entirety of the pond. Compaction specifications should be
carefully selected as soils with such high silt content used in a berm or dam may be subject to
"piping" or erosion around macropores which can result in significant leakage. The degree and
type of compaction is not suggested here, as design specifications are not within this consultant's
scope.
Hargett Resources, Inc.; 408 Deepwood Drive, Greer, SC 29651
Phone [phone] dhurgert520)grnad.conr

1 Henderson County Public Schools., Soils Investigation — Mills River Elementary School, 31 December 2007, p. 6 of 6
1 Summary
1 This report presents the methods and results of a limited scope of investigation, site
characterization, and measurement of soil hydraulic properties performed at the MRES. This
assessment is intended to support proposed design concepts for management of stormwater for
the proposed new school facilities. Based on the results of this limited investigation, soil
conditions do appear to be generally compatible with the concept of using retention ponds
constructed in the natural soils, with appropriate compaction. However, the soil conditions at the
MRES site are problematic for the use of bioswales intended to infiltrate stormwater at any
significant rate. The ultimate performance of both bioswales and retention pond features will
depend on the specifics of designs, hydraulic loading, and proposed capacity. The functionality
and performance of these features may potentially be enhanced by making some modifications to
the designs, and to the soils. The limitations of these soils may potentially be overcome with
design modifications, but alternative approaches to bioswales may be well advised.
Qualifications to this Report
This letter report is qualified in that the stormwater management features proposed for the MRCS
site have not yet been finalized. Further, the purpose of this investigation was to assess the
general suitability of site soils for the stormwater concepts proposed, and not to provide specific
design data. These caveats notwithstanding, the work presented in this report provides a useful
foundation for decision making with regard to the proposed stormwater facilities dependent upon
natural soil properties.
1
1
0
1
I
I would be pleased to respond to any questions regarding the findings presented in this report or
to provide ongoing technical assistance with this project.
I thank you for the opportunity to contribute to this project and look forward to continued
collaboration with your project team as needed.
Sincerely yours,
David L. Hargett, Ph.D�)
Principal and Senior Consultant
Certified Professional Soil Scientist 1 Soil Classil
Certified Ground Water Professional (AGWSE #
Licensed Soil Scientist (NC LSS # 1139)
Attachments: Figures
Tables
cc: Brian Dey, McKim & Creed (w/ Attachments, via Regular Mail)
Hargett Resources, Inc., 408 Deepwood Drive, Greer, SC 29651
Phone [phone] dhciigeu52(a-)gnuril.c•otn
1

� M M M M M M M M M M M M M M M M M M
�XISINII"
Legend BUILDiNG
X Proposed Test Location
♦ Test Pit Location
Ksat Location
N
r
L�
fL
Area 4
sat
#4+
rea
j,.,j 'r t
Area
Not to Scale
`T
r& -7 -1
Figure 1: Mills River Elementary School, L.. .n . :r
Approximate Locations of Test Pits
and Hydraulic Conductivity Testing
REMENTARY
SCHCXX
7IL1349
(MOPONO)
ITE2111M)

Apr
FIRET
PS
lip
4P lot
flip

Soil Map —Henderson County, North Carolina
(Mills River ES, School Rd, Mills River)
MAP LEGEND
MAP INFORMATION
Area of Interest
(AOI)
( Very Stony Spot
Original soil survey map sheets were prepared at publication scale.
Area cf Interest (AOI)
Viewing scale and printing scale, however, may vary from the
tr wet Spot
original. Please rely on the bar scale on each map sheet for proper
Soils
A Other
map measurements.
Soil Map Units
Special Line Features
Source of Map: Natural Resources Conservation Service
Special
Point Features
Gully
Web Soil Survey URL: http://websoilsurvey.nres.usda,gov
Blowout
Coordinate System: UTM Zone 17N
Short Steep Slope
®
Borrow Pit
This product is generated from the USDA-NRCS certified data as of
Other
the version date(s) listed below.
x
Clay Spot
Political Features
Soil Survey Area: Henderson County, North Carolina
Closed Depression
Municipalities
P
Survey Area Data: Version fi, Jan 19, 20D7
}:
Gravel pit
p Cities
Dates) aerial images were photographed: 3/1911994; 311511998
Gravelly Spot
a Urhan Areas
The orihophoto or other base map on which the soil lines were
Landfill
water Features
compiled and digitized probably differs from the background
Oceans
imagery displayed on these maps, As a result, some minor shifting
?,
Lava Flow
of map unit boundaries may be evident.
41,,
Marsh
-- Streams and Canals
4
Mine or Quarry
Transportatlan
+-a+ Rails
®
Miscellaneous Water
Roads
Q.
Perennial Water
�y Interstate Highways
Rock Outcrop
US Routes
f
Sailne Spot
State Highways
Sandy Spot
�y Local Roads
Severely Eroded Spot
Other Roads
0
Sinkhole
11
Slide or Slip
it
Sodic Spot
Spoil Area
n
Stony Spot
USDA Natural Resources Web Soil Survey 2.0 1215/2007
;1l Conservation Service National Cooperative Soil Survey Page 2 of 3

Soil Map —Henderson County, North Carolina
Map Unit Legend
Mills River ES, School Rd, Mills River
Henderson County, North Carolina (NC089)
Map Unit Symbol
Map Unit Name
Acres in Apt
Percent of AOI
BaB
Bradson gravelly loam, 2 to 7
percent slopes
0.0
0.0%
DeA
Delanco (Dillard) loam, 0 to 2
percent slopes
15.8
15.3%
DeB
Delanco (Dillard) loam, 2 to 7
percent slopes
12.0
11.7%
FaC
Fannin sill loam, 7 to 15 percent
slopes
75.3
73.0%
Totals for Area of Interest (AOI) 103.1 100.0%
t!5DA Natural Resources Web Soil Survey 2.0 12/5/2007
.7 Conservation Service National Cooperative Soil Survey Page 3 of 3

1 Official Series Description - FANNIN Series
http://www2.ftw.nrcs,Llsda.gov/osd/dal/F-/FANNIN,htnil
LOCATION FANNIN NC+GA SC TN
Established Series
AG; Rev. MKC
03/2003
FANNIN SERI]ES
The Fannin series consists of very deep, well drained soils on gently sloping to very steep ridges and
side slopes of the Blue Ridge (MLRA 130). They formed in residuum that is affected by soil creep in
the upper part, and is weathered from high-grade metamorphic rocks that are high in mica content such
as mica gneiss and mica schist. Mean annual temperature is 52 degrees F., and mean annual rainfall is
about 52 inches near the type location. Slopes are 6 to 95 percent.
TAXONOMIC CLASS: fine -loamy, paramicaceous, mesic Typic Hapludults
TYPICAL PEDON: Fannin loam --forested. (Colors are for moist soil unless otherwise stated.)
Oe--O to 1 inch; very dark brown (10YR 2/2) moderately decomposed organic material containing some
mineral soil; strongly acid; abrupt wavy boundary.
A-- l to 4 inches; brown (7.5YR 5/2) loam; weak fine granular structure; very friable; many fine and
medium roots; common flakes of mica; few quartz gravel; strongly acid; clear smooth boundary. (2 to 8
inches thick)
' E--4 to 8 inches; brown (7.5YR 514) loam; weak fine and medium granular structure; very friable; many
fine and medium roots; common flakes of mica; few quartz gravel; strongly acid; clear smooth
boundary. (0 to 6 inches thick)
Bt1--8 to 14 inches; yellowish red (5YR 516) clay loam; weak fine subangular blocky structure; friable;
slightly sticky and slightly plastic; few medium and fine roots; common flakes of mica; strongly acid;
clear smooth boundary.
Bt2--14 to 26 inches; red (2.5YR 4/6) clay loam; moderate medium subangular blocky structure; friable;
sticky; slightly plastic; common distinct clay films on faces of peds; many fine and medium flakes of
mica give greasy feel; some are soft and easily crushed by rubbing; strongly acid; gradual wavy
boundary. (Combined thickness of the Bt horizon is 10 to 30 inches.)
BC--26 to 33 inches; yellowish reel (5YR 518) loam; weak medium subangular blocky structure; friable;
few distinct clay films on faces of peds; many Fine and medium flakes of mica most of which are soft;
common small fragments of saprolite; strongly acid, gradual irregular boundary. (2 to 15 inches thick)
C- 33 to 61 inches; yellowish red (5YR 5/8) mica schist saprolite that has a texture of loam; few distinct
' reddish clay films on cleavage planes; friable; strongly acid.
TYPE LOCATION: Alleghany County, North Carolina; one mile west of Edwards' Crossroads, 0.2
mile south of Zion Church, in cut over hardwood area 100 feet east of county road.
RANGE IN CHARACTERISTICS: Solum thickness ranges from 20 to 45 inches. Depth to lithic or
paralithic contact is more than 60 inches. Content of coarse fragments range from 0 to 35 percent in the
A and C horizons and from 0 to 25 percent in the B horizons. Fragments are dominantly gravel in most
pedons but cobbles are dominant in some pedons. Reaction is very strongly acid to slightly acid.
1 1 of 3 2007.12.30 4:16 PM
1

Official Series Description - FANNIN Series http:/lwww2.ftw.nres.usda.govlosd/daUF/FANNEN.htm1
1 Content of flakes of mica is common or many in the surface layer and upper B horizon and is many in
the lower B and C horizons.
The A or Ap horizon has hue of 7.5YR or IOYR, value of 3 to 5, and chroma of 2 to 4. Where value is
3 or less, this horizon is less than 7 inches thick.
The E horizon, where present, has hue of 7.5YR or IOYR, value of 5 or 6, and chroma of 4 to 8. It has
the same texture as the A horizon in slightly eroded pedons.
The BA or BE horizon, where present, has hue of 5YR or 7.5YR, value of 4 or 5, and chroma of 4 to 6.
1 It is loam, fine sandy loam or silt loam in the fine -earth fraction.
The Bt horizon has hue of 2.5YR or 5YR, value of 4 or 5, and chroma of 4 to 8. Mottles, if they occur,
are in shades of red, yellow, or brown. The Bt horizon is loam, silty clay loam, clay loam, or sandy clay
loam in the fine -earth fraction.
The BC horizon is similar in color to the Bt horizon. It is loam, fine sandy loam, sandy loam, or sandy
clay loam in the fine -earth fraction.
' The C horizon is similar in color to the BC horizon or is multicolored. It is saprolite weathered from
high-grade metamorphic rocks having a high content of mica such as mica gneiss and mica schist. It has
a texture of loam, sandy loam, fine sandy loam, loamy sand, or loamy fine sand in the fine -earth
fraction.
COMPETING SERIES: The Wat.amm series is the only other series in this family. The, Brownwood,
Cashiers, Chandler, Grover, Manor, Micaville, and Mt. Airy series are in closely related families.
Watauga soils have Bt horizons of 7.5YR or yellower hues. Brownwood, Cashiers, Chandler, Manor,
Micaville, and Mt. Airy soils do not have an argillic horizon. In addition, the Mt. Airy soils have more
than 35 percent coarse fragments in the particle -size control section. Brownwood is moderately deep and
Micaville is deep to a paralithic contact. Grover soils are in a thermic soil temperature class.
GEOGRAPHIC SETTING: Fannin soils are gently sloping to very steep and are on ridges and side
slopes in the Blue Ridge (MLRA 130). They formed in residuum that is affected by soil creep in the
upper part, and is weathered from high-grade metamorphic rocks having a high content of mica such as
mica gneiss and mica schist.. Slopes range from 6 to 95 percent. Elevation ranges from about 1,400 to
3,500 feet. Mean annual air temperature ranges from 46 to 57 degrees F., and mean annual rainfall
ranges from 45 to 65 inches.
GEOGRAPHICALLY ASSOCIATED SOILS: In addition to the competing Brownwood, Cashiers,
' Chandler, Manor, Micaville, and Watauga series, these are the Brevard, Chestnut, Clifton, Cowee,
Edneyville, Evard, Ha esvi lie, Saunook, Tate, Thunder, and TUSQuitee series. Brevard, Saunook, Tate,
Thunder, and Tusquitee formed in colluvium, have less mica, and are in coves. Brownwood, Cashiers,
Chandler, Chestnut, Clifton, Cowee, Edneyville, Evard, Manor, Micaville, and Watauga soils are on
ridges and side slopes. In addition, the moderately deep Chestnut and the very deep Edneyville soils
contain less mica and have a cambic horizon. The moderately deep Cowee and very deep Evard soils
contain less mica. Clifton and Hayesville soils are in a fine particle -size class.
' DRAINAGE AND PERMEABILITY: Well drained. Runoff is slow under forest cover and is
medium to rapid in areas where the forest cover is removed. Medium internal drainage; moderate
permeability.
USE AND VEGETATION: Most areas are in forest. Common trees are chestnut oak, scarlet oak,
black oak, white oak, hickory, eastern white pine, Virginia pine, and pitch pine. Yellow poplar and
northern red oak are common in the northern portions of MLRA 130. The understory includes
flowering dogwood, American chestnut sprouts, flame azalea, blueberry, buffalo nut, mountain laurel,
2 of 3 2007.12.30 4:16 PM

Official Series Description - FANNIN Series http://www2.ftw.nres.usda.gov/osd/dat/F/FANNIN.htm]
' rhododendron, and sourwood. Cleared areas are principally used for pasture and hayland. Small areas
are used for growing corn, small grain, truck crops, apples, and Christmas trees.
DISTRIBUTION AND EXTENT: Blue Ridge (MLRA 130) of North Carolina, Georgia, South
Carolina, and Virginia. The series is of moderate extent.
MLRA OFFICE RESPONSIBLE: Lexington, Kentucky
1 SERIES ESTABLISHED: Fannin County, Georgia; 1923.
REMARKS: Fannin series was formerly classified in the Red -Yellow Podzolic great soil group.
Available data show that the Fannin soils have average clay content of less than 35 percent in the Bt
horizons, average silt content of 20 to 50 percent in the upper 20 inches of the Bt horizons, and much
mica throughout the sola. These soils feel as if they are higher in silt than mechanical analyses shows
' them to be. They have a greasy feel caused by the high mica content. The mica is dominantly soft and
mineral structure is destroyed by prolonged rubbing.
Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - the zone from the surface to 8 inches (Oe, A, and E horizons)
Argillic horizon - the zone from 8 to 33 inches (Btl, Bt2, and BC horizons)
High content of flakes of mica in the Bt2, BC, and C horizons
ADDITIONAL DATA:
SIR = NC0020, NCO278 (Eroded) MLRA = 130
National Cooperative Soil Survey
U.S.A.
I
I
I
L,
13of3
2007,12.30 4:16 PM
I

Figure 3A: Test Pit # 1 Figure 3B: Test Pit # 2
Mills River Elements School Horse Shoe, NC: Soils Investigation��
ry

17.,. -
���/,{.
}.. •• v � '�j` ak ;fir 4 � i �c �'_iY fac,; r �i�
�it�r z tr 'r�7 ` � ' 1 : • y � '
fm j -�[y ,�.-�y •r: r�r';: �yy�''��ar
$•.F
t79 Ri

® M M ® ® ® ® ® ® M ® ® = O ® M ® M
SITE: MILLS RIVER ELEM SCHOOL
LOCATION: School House Rd, Horse Shoe
COUNTY.- Henderson, NC
RJAPOSE: Stormwater Infiltration/Retention Systems
Table 1
Typical Soil Profile Description and Interpretations
PROFILE: Test Pit # 01 - (Typical of Site Soils)
GROUND SURFACE ELEVATION: - 2120 ft msl
DESCRIED BY. D.L. Hargett, PhD, LSS
INTERPRETED BY. D.L. Hargett, PhD, LSS
OTHERS PRESENT- NA
DATE: 1 1-Dec-07
PHOTO ft Appended
SOIL SERIES: Not classified -see Comment 3.
DEPTH (in)
SOIL TEXTURE
SOIL TEXTURE (Unified)
STRUCTURE / CONSISTENCY
SOIL COLOR
SOIL COLOR
ESTIMATED
PERCOLATION TEST
REMARKS
(USDA)
(PRIMARY)
(SECONDARY)
HYDRAULIC
(min/in) ACTUAL or
CONDUCTIVITY
ESTIMATED
0-9
loam
sandy silt to silty sand
weak fine to medium granular structure;
(10YR4/4) dark.
none
50-100
not estimated
Topsoil zone.
(ML-SM)
very friable; many fine roots
yellowish brown
9-18
silt loam
silty sand (SM)
weak medium subangular blocky
(10YR5/3)
none
20-100
not estimated
structure; friable; common fine & medium
rnntq
brown
18-29
loam to silt loam
sandy silt to silty sand
moderate medium subangular blocky
(7.5YR6/3) light
(7.5YR7/2) light
2-20
ESTIMATED 60-120
Faintly mottled.
(ML-SM)
structure; firm; few fine & medium roots;
few mica flakes
brown
gray
miR/in
29-44
loam to silt loam
sandy silt to silty sand
moderate medium subangular blocky
(10YR6/2) light
(10YR6/6)
2-20
ESTIMATED -60-
Gleyed matrix below 29 in.
(ML-SM)
structure becoming massive with depth;
brownish gray
brownish yellow
120i- min/in
indicative of seasonal saturation.
44-78+
loam to silt loam
sandy silt to silty sand
massive weathered saprolite structure;
(10YR6/2) light
(10YR6/6)
2-20
ESTIMATED -60-
Gleyed and mottled zone with
(ML-SM)
extremely firm but crushes with effort to
brownish gray
brownish yellow
120+ min/in
massive structure parting to
loamy texture; no rock structure evident
coarse angular blocks.
to test pit bottom at 78"; no refusal w/
bedrock probe to 1 50"; profile unusually
Comment 1: Seasonal saturation indicated at depth as shallow as 28 in. per mottling and gleying with depth.
Comment 2: No refusal due to residual bedrock indicated by bedrock probe to 150 inches. No resistant rock structure in C horizons. Test pit terminated at 78 in.
Comment 3: Area mapped as Fannin series but all test pits have morphology and internal drainage characteristics wetter than typical of Fannin.
p.1of1

Table 2
Soils Investigation -Test Pit Descriptions
Mills River Elementary School - Henderson County Public Schools
Proposed Stormwater Infiltration / Retention Facilities
Investigation Date: 11-12 December 2007 By: D.L. Hargett, Ph.D., LSS
Test Pit
Depth Zone in
Texture USDA
Texture Unified
Primary Color
Comments
1
0-9
loam
sandy silt to silty
10YR4/4
Mottled below 18 in. Gleyed
sand ML-SM
below 29 in. Subangular blocky
structure to 44 in., massive
9-18
silt loam
sandy silt (ML)
10YR5/3
below. Indications of seasonal
18-29
loam to silt loam
sandy silt to silty
7.5YR6/3 .
sand ML-SM
saturation at - 30 in. or
shallower. Bedrock probe to
29-44
loam to silt loam
sandy silt to silty
10YR6/2
sand ML-SM
150 in. - no refusal.
44-78
loam to silt loam
sandy silt to silty
Variegated - all
sand ML-SM
colors above
2
0-6
loam
sandy silt to silty
10YR4/4
Mottled below 18 in. Gleyed
sand ML-SM
below 28 in. Subangular blocky
6-18
loam to silt loam
sandy silt to silty
10YR6/6
structure to 48 in., massive
sand ML-SM
below. Indications of seasonal
saturation at - 28 in. or
18-28
silt loam
silty sand to clayey
10YR7/6
sand (SM-SC)
shallower. Bedrock probe to
144 in. - no refusal.
28-48
loam to silt loam
sandy silt to silty
10YR7/2
sand ML-SM
48-72
loam to silt loam
sandy silt to silty
10YR7/2
sand ML-SM
3
0-40
sandy loam to
sandy silt to silty
10YR5/3
Mixed fill - extremely variable to
silt loam fill
sand (ML-SM)
mixed fill
40 in. Original topsoil with many
large roots at 40-46 in. Natural
40-46
loam
sandy silt to silty
10YR4/4 (buried
sand ML-SM
topsoil)
profile below 46 in. Bedrock
probe to 120 in. - no refusal.
46-60
loam to silt loam
sandy silt to silty
10YR6/6
sand ML-SM
4
0-12
fine sandy loam
silty sand (SM)
10YR4/3
Compact topsoil zone. Mottled
below 12 in. Gleyed below 38
12-22
loam to clay
sandy silt to silty clay
10YR6/2
loam
(ML-CL)
in. Subangular blocky structure
to 38 in., massive below.
Indications of seasonal
saturation at - 38 in. or
shallower. Bedrock probe to
144 in. - no refusal.
22-38
loam to clay
loam
sandy silt to silty clay
(ML-CL)
10YR6/4
38-72
silt loam
sandy silt to silty
sand (ML-SM}
10YR7/2
p. 1 of 1

1
1
I
1
Table 3
Summary of Soil Hydraulic Conductivity Properties
Mills River Elementary School
Henderson County Public Schools
Test #
Area 1
Zone
Soil Texture
Hydraulic
Comments
Application
Tested
Conductivity
Depth
Ksat
(inches
USDA
Unified
(cmlhr)
(cm/day)
below
rade
1
Bioswale
24-34
Silt
silty fine
1.801
43.22
Ksat value
loam
sand to
may be
clayey silt
anomalously
high due to
— slightly
sli g y
root channel
plastic
or krotovina
MH-ML
2
Retention
40-50
Silt
silty fine
0267
6.40
Dense,
Pond
loam
sand to
gleyed
clayey silt
material,
— slightly
apparently
seasonally
plastic
saturated
MH-ML
3
Bioswale
26-36
Silty
clayey silt
0.067
1.60
Extremely
clay
— slightly
compact in
loam
plastic
area ofexisting
(MH)
drainage
Swale
4
Retention
52-60
Silty
clayey silt
0.038
0.92
Laboratory
(Lab)
Pond
clay
— slightly
Ksat on
(from
loam
plastic
Undisturbed
TP
(MH)
Pedestal of
Soil
#1
Note: Tests 1-3 were performed using a modified constant -head permeameter
and the Glover solution for calculation of hydraulic conductivity. Test 4 was
performed on an undisturbed pedestal of soil removed from test pit #3, coated
with hydraulic cement, and transported to the lab for determination of hydraulic
' conductivity using a constant -head set-up.
I
P. 1 of 1
1

Stormwater Management Narrative
For
MILLS RIVER ELEMENTARY SCHOOL
Town of Mills River
Henderson County, North Carolina
1.0 INTRODUCTION
The project site is located in the Town of Mills River in Henderson County and
consists of 13.84 acres. Improvements include the construction of a one-story 78,134 s.f.
elementary school, surface parking, a water quality detention pond, and associated site
improvements that will disturb approximately 8.36 acres.
The drainage basin, including off -site and on -site, totals approximately 11.50
acres that will drain into the new detention pond. This following narrative outlines the
details of the stormwater management plan.
2.0 SITE DESCRIPTION
Mills River EIementary is an existing school site that includes many existing
buildings and associated parking. The site is located on the Southwest corner of the
School House Road and Banner Farm Road intersection. The post -developed site will
include the new one-story, 78,134 s.f. school building, surface.parki.ng, stormwater
detention pond, and as well as the existing buildings/site improvements. Several of the
existing buildings will be demolished in phases, in order to construct additional
parking for the new/remaining buildings. Our stormwater management plan models
the worst case scenario to ensure adequate stormwater measures are installed.
Runoff of the site flows to the southwest corner of the site into a small ditch that
runs through the site. According to Henderson County the entire drainage area has a
soil classification of FaC. Erosion control measures will be used during all phases of
construction to prevent sediment run off from the project site.
3.0 STORMWATER MANAGEMENT
The 11.50 acre drainage area will generate a total system flow of 48.58 cubic feet per
second (cfs) during the ten year storm. This flow will be collected by catch basins and
drop inlets installed throughout the site. The direction of the flow in the storm system
is kept constant with the natural topography, by channeling the flow to the Southwest
corner of the project site. At the end of the storm pipe network, the flow will outlet into
a water quality pond.

i
Stormwater Management Narrative for Mills River Elementary School January 9,2008
Henderson County, North Carolina Page 2
The stormwater network was designed using flow rates from the 10-year storm
event, which was modeled by Bentley StormCAD v5.6 computer software. The water
duality pond drains to a level spreader and filter strip. To exit the site, the flow will
travel in to an existing ditch that runs through the corner of the site. The ditch
ultimately feeds into the Boylston Creek, which is a portion of the French Broad River
Basin.
4.0 SUMMARY
The project site's stormwater network will be able to handle the stormwater runoff
of a 10-year storm event. The entire drainage area is collected using strategicaIIy
installed catch basins and drop inlets to avoid run-off to neighboring sites, while also
treating and filtering the flow in the water duality pond. Therefore, the new
development should not have an adverse impact on the downstream and adjacent
properties.
5.0 DETENTION POND MAINTENANCE
On a monthly basis, the detention basin will -be inspected. Grass will be mowed
regularly and shall not exceed a height of six inches. Trees will not be permitted to
grow within the basin.. Trash is to be removed in and around the pond. Sediment
accumulations will be removed and the pond will be regraded to provide proper
drainage towards the outlet discharge. Erosion of side slopes, if present, shall be
addressed. The outlet structure and pipe will be inspected and -cleaned of all sediment
and debris. Damages. to the outlet structure and pipe will be repaired.