SWA000080_DEQ Combined Report Stormwater and Erosion_20201023

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Stormwater & Erosion Narrative

Tyson Griswold, PE
Griswold Engineering & Environmental, PLLC

HILLS MACHINERY &
ASSOCIATED LEASE
BUILDINGS

MILLS RIVER, NC

1

Table of Contents

Narrative ......................................................................................................................................................................... 3

Project Description ............................................................................................................................................... 3
Site Description and Adjacent Properties ....................................................................................................... 3
Stormwater Discharge .......................................................................................................................................... 4
Soils .......................................................................................................................................................................... 4
Primary References .............................................................................................................................................. 5
Stormwater Calculations ................................................................................................................................................ 6
Design Volume Calculations .............................................................................................................................. 6
Pre-Development Runoff vs. Post-Development Runoff ............................................................................ 6
Water Quality Flow ................................................................................................................................................ 7
Erosion and Sediment Control ....................................................................................................................................... 7
Site Data ................................................................................................................................................................... 7
Skimmer Basin (from 6.64 of the NC Erosion Control Manual) ................................................................. 7
Diversion Ditch Velocity Calculation ................................................................................................................ 8
Outfall Protection .................................................................................................................................................. 8
Appendix ......................................................................................................................................................................... 9

2

Narrative

Project Description

J&A Land Development, LLC is proposing a 3 total buildings in the first phase of construction,
and a future building in a future phase, at 5475 Old Haywood Road (Highway 191) in Mills River,
Henderson County, North Carolina. The location is 1 ¼ miles north of the intersection between
Boylston Highway (US 280) and Old Haywood Road (NC 191) on the west side of the road. The
4 proposed buildings are all 10,400 square feet. The Hills Machinery building will be a heavy
vehicle rental and sales office, and will have a wash station with an oil and water separator. All
water from the wash station is to be routed through the onsite septic system. Approximately 6.7
acres are to be disturbed to complete the project. The following engineering report covers
stormwater and construction erosion elements. In order to begin construction, approvals are
needed for stormwater BMPs for treatment and post-construction peak flow attenuation, and
erosion control for construction conditions.

Site Description and Adjacent Properties

The subject site is located 5475 Old Haywood Road in Mills River, North Carolina. The site
consists of one parcel of land, identified by the Henderson County Tax Assessor as Parcel
Number 96324479133, totaling approximately 12.07-acres. Surrounding properties typically
consists of residential, commercial and agricultural developments. Based on our review of
publicly available current and historical aerial photography, the property has primarily been
utilized as an agriculture field with the exception of an approximate 1,000 square foot modular
building and associated asphalt parking area located on the east side of the property which was
constructed sometime between April 2020 and October 2005. Generally speaking, the existing
topography slopes to the east with an elevation difference estimated to be approximate 10 to 15
feet across the site. The topography around the existing structure is relatively level. There were
no visible rock outcroppings or groundwater springs apparent on the property at the time of
our site visit. The on-site building was noted to be a typical commercial modular type office
structure. The existing parking and drive area appeared to be in good condition, based on our
site observations.

Project Data

The proposed project includes the following findings:
3 commercial buildings and associated parking for phase 1.
1 future building and associated parking for phase 2.
All stormwater and erosion control measures were sized with the future building taken into
consideration.
The parcel is approximately 12.07 acres with approximately 6.7 acres disturbed.
Total Impervious Added = 3.43 acres
o Total Concrete & Roof = 1.53 acres
o Total Gravel = 1.90 acres

3

The added impervious area is > 24% of the drainage site. Per NC DEQ Stormwater
Design Manual, stormwater treatment is provided, which removes Total Suspended Solids
from stormwater runoff.
Stormwater Treatment: Bioretention
o Due to site advantages and intended use, a bioretention cell was chosen to provide
efficient removal method of suspended solids, heavy metals, adsorbed pollutants,
nitrogen, phosphorus, pathogens, and temperature. Not only does a bioretention
cell provided treatment of the above pollutants, this BMP also provides excellent
peak flow attenuation, which adds to the longevity of the stormwater treatment
infrastructure, and provides long term stability to the site.
o This design flow from the 1” is shown in the attached HydroCad model to be
considered “discarded” flow through the media.
o Bioretention media was not included in storage consideration for better long-term
performance. Media was assumed to have a 2 in/hr exfiltration of the water quality
event.
o The Discrete NRCS Curve number method was used to determine design volume.
3
The design volume is 4,984 ft which provides for an area of approximately 5,000
2
ft for the bioretention basin configuration.
Peak Flow Attenuation
o Overall this development provides for a slight flow reduction for post-development
flow from pre-development flows. Post--development flows.
o Riser flows were checked with HydroCAD. Flows from the 10-year, and 25-year
storm safely pass through the 18” outfall culvert in the riser structure.
o A 10’ long emergency overflow is provided at elevation 2170.
3
o Approximately 30,000 ft of storage is provided.
Stormwater Collection
o A 6-pipe stormwater collection system collects the stormwater from the impervious
areas to ensure storm flow routing to the bioretention basin.
o Total length of pipe:
18” RCP = 991’
24” RCP = 230’
o The pipe network was modeled as catch basins in HydroCAD in accordance with
recommended procedures.
o The depth of flow for the 25-year, 24-hour storm in the main collector 24” pipe was
calculated to be 1.37’ deep, with a velocity of 4.1 fps.

Stormwater Discharge

The overall discharge point is the ditch along Highway 191, Old Haywood Road. This ditch then
routes to an unnamed tributary of McDowell Creek.

Soils

Included in the report is a soils evaluation from a licensed soil scientist. The evaluation revealed
that the soils are relatively uniform and homogenous throughout the proposed basin area

According to the soil scientist’s report and a Web Soil Survey Soil Investigation (See Appendix),

4

the soil series in the area are predominantly mapped as Hayseville Sandy Loam is very deep,
well drained and moderately permeable. Moderate permeability is defined by the NRCS as 2.0-
6.0 inches per hour. The depth to the most restrictive layer of soil, which is natural groundwater,
is noted to be more than 80 inches. The capacity of the most restrictive layer of soil to transmit
water is moderately high to high. There isn’t a natural frequency to flood or pond.

For the purposes of the stormwater model, an exfiltration rate of 2.0 inch per hour is assumed
since this is the exfiltration rate of the bioretention media.

Primary References

Stormwater treatment design meets the requirements of the North Carolina DEQ Stormwater
BMP and Design Manual which can be found at https://deq.nc.gov/sw-bmp-manual.
Erosion Control Design meets the requirements of the North Carolina DEQ Erosion and
Sediment Control Design Manual which can be found at
https://deq.nc.gov/about/divisions/energy-mineral-land-resources/energy-mineral-land-permit-
guidance/erosion-sediment-control-planning-design-manual.

5

Stormwater Calculations

Design Volume Calculations

Per the stormwater calculations guidance in the NC DEQ Stormwater Design manual, the
Discrete NRCS Curve Number method for determining the design volume was utilized for BMP
sizing. Calculation below shows design volume determination for the 1” design storm:

Weighted CN = 92 (Concrete, roof, gravel)

S = = 10

S= 0.87

()
.^
Q* =
(.)

Q* = 0.4

2
D = Q* x Area (ft)
v
12

33
D = 4926 ft = 5000 ft
v

Pre-Development Runoff vs. Post-Development Runoff

Since the bioretention cell is an excellent BMP for peak flow attenuation, we utilized a base
dimension for the basin of L = 100’ & W = 50’. With the configuration of the riser structure and
the requirements for bioretention construction, the basin provides for peak flow attenuation for
the 10-year, 24-hour & 25-year, 24-hour storm. As noted above, the HydroCAD model shows a
slight reduction in runoff for post-development flow, compared to the pre-development flow.
See HyrdoCAD report in the Appendix for calculations. Below is the pre-development flow that
was calculated compared to the post-development flow for both the 10-year, and 25-year storms:

10-year, 24-hour P = 5.09”

Pre-Development Flow = 15.72 CFS
Post-Development Flow = 15.61 CFS

25-year, 24-hour P = 5.94”

Pre-Development Flow = 19.35 CFS
Post-Development Flow = 15.97 CFS

6

Water Quality Flow

The Water Quality Flow (P=1”) is shown by the model as exfiltration, and is considered discarded
and not running through and outlet structure. The model shows, that all of the flow for a 1” rain
event is exfiltration through the media and soil. It also shows that no flow is going through the
riser structure for a 1” rainfall.

Note: All calculations for storm flow and runoff volume were modeled in HydroCAD
utilizing the TR-20 NCRS method for determining storm flow.

The runoff volume for the remaining undisturbed area was considered utilizing the NRCS
Discrete Method. It was determined using this method that flows from the undisturbed area is
negligible and most likely will be flowing away from the stormwater BMP, and was therefore not
included in the analysis.

Erosion and Sediment Control

Site Data
Drainage area – 6.7 Acres of disturbed area of 12.07 total acres in the parcel. This is the
basic site that we have. All flow from areas above the site are considered negligible. See
rationale in Adjacent Property in above narrative.
Disturbed Area – 6.7 Acres
P = 5.04” for 10-year, 24-hour rainfall depth from NOAA
Cleanout Interval – 30 days

Flow from the entire site for 10-year, 24-hour storm = 14 CFS by HydroCAD TR-20 method.
Time of Concentration for all areas was calculated and is in the HydroCAD report in the
Appendix.

Due to the layout and size of the land, as well as the proposed construction sequence, a total of
3 erosion control structural measures are proposed. One skimmer basin is to be located in the
area of the proposed bioretention basin. This skimmer basin will be converted to a bioretention
basin near the end of construction and after site stabilization. This results in the skimmer basin
being oversized for sediment control purposes.

As shown below, more than enough storage is provided for the 10-year, 24-hour rain event for
the construction period when the site is assumed to be in a cut condition.

Skimmer Basin (from 6.64 of the NC Erosion Control Manual)

2
Minimum Surface Area for Skimmer Basin = 325 ft per 1 cfs of 10-year, 24-hour storm
Q = 14 CFS
10
2
Minimum Area = 14 CFS * 325ft
2
Minimum Area = 4,550 ft
2
Area provided = 4,824 ft

7

3
Minimum Volume Required for Skimmer Basin = 1800 ft for 1 acre of Disturbed Area draining to
the measure.
Disturbed Area = 5.9 Acres
3
Minimum Volume = (5.9 Acres) *1800 ft
3
Minimum Volume = 10,620 ft
3
Volume provided = 12,972 ft

Skimmer Orifice Diameter
Q = and D = x H
D
,
Q =
D
Q = 1980
D

Try 1.5” skimmer with H = 0.125’ (from Table 6.64a)

D = x 0.125

D = 0.3”

Use 1.5” diameter skimmer

Diversion Ditch Velocity Calculation

The velocity was checked in HydroCAD for the diversion ditches and all calculated flows in the
diversion ditches are under the required 7 ft/s. See appendix for calculated flows.

OutfallProtection

From NCDEQ Erosion Control Design Manual Figure 8.06a. Maximum flow from the outfall is
approximately 15 CFS. At that flow:

D = 1.5’
O
3D= 4.5’
O
L = 15’
a
W = 16.5
d = 6”
50

See appendix for copy of Figure 8.06a.

8

Appendix
9

6S
Future Building
1S
CB
7P
Pre Devolment
Condition
12S
Pipe 4 18"RCP
CB
3P
Main Gravel Area
2S
CB
Pipes 1,2,5,6
13S
8P
Hills Machinery Sub
Area
Lease 2 Future Gravel
Pipe 3 24" RCP
10S
CB
5P
Lease Space 2
4S
Pipe 7 18"RCP
Lease Space 1 Sub
Basin
9P
Bioretention
Routing Diagram for Hills Machinery Stormwater R3
Reach
SubcatPond
Link
Prepared by HP, Printed 10/8/2020
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC

EROSION and SEDIMENTATION CONTROL PLAN PRELIMINARY REVIEW CHECKLIST

The following items shall be incorporated with respect to specific site conditions, in an erosion & sedimentation control plan:

NPDES Construction Stormwater General Permit NCG010000
X
______ Designation on the plans where the 7 or 14 day ground stabilization requirements apply per Part II.E.1 of the permit.
X
______ Design of basins with one acre or more of drainage area for surface withdrawal as per Part II.B.8 of the permit.

X
LOCATION INFORMATION _____ Name and classification of receiving water course or name of
municipal operator (only where stormwater discharges are to
X
______ Project location & labeled vicinity map (roads, streets, landmarks) occur)
X
______ North arrow and scale
X
______ Identify River Basin.
STORMWATER CALCULATIONS
N/A
______ Provide a copy of site located on applicable USGS quadrangle and

X
NRCS Soils maps if it is in a River Basin with Riparian Buffer _____ Pre-construction runoff calculations for each outlet from the site (at
requirements. peak discharge points). Be sure to provide all supporting data for
the computation methods used (rainfall data for required storm
GENERAL SITE FEATURES (Plan elements) events, time of concentration/storm duration, and runoff
coefficients).
XX
_____ Property lines & ownership ID for adjoining properties _____ Design calculations for peak discharges of runoff (including the
X
_____ Existing contours (topographic lines) construction phase & the final runoff coefficients for the site)
XX
_____ Proposed contours _____ Design calcs for culverts and storm sewers (include HW, TW and
X
_____ Limits of disturbed area (provide acreage total, delineate limits, outlet velocities)
X
and label). Be sure to include all access to measures, lots that will _____ Discharge and velocity calculations for open channel and ditch
be disturbed, and utilities that may extend offsite. flows (easement & rights-of-way)
XX
_____ Planned and existing building locations and elevations _____ Design calcs for cross sections and method of stabilization for
X
_____ Planned & existing road locations & elevations, including existing and planned channels (include temporary linings). Include
temporary access roads appropriate permissible velocity and/or shear stress data.
XX
_____ Lot and/or building numbers _____ Design calcs and construction details for energy dissipaters below
X
_____ Hydrogeologic features: rock outcrops, seeps, springs, wetland culvert and storm sewer outlets (include stone/material specs &
and their limits, streams, lakes, ponds, dams, etc. (include all apron dimensions). Avoid discharges on fill slopes.
X
required local or state buffer zones and any DWQ Riparian Buffer _____ Design calcs and dimension of sediment basins (note current
determinations) surface area and dewatering standards as well as diversion of
x
_____ Easements and drainageways, particularly required for offsite runoff to the basins). Be sure that all surface drains, including
affected areas. Include copies of any recorded easements and/or ditches and berms, will have positive drainage to the basins.
agreements with adjoining property owners.
x
_____ Profiles of streets, utilities, ditch lines, etc. VEGETATIVE STABILIZATION
x
_____ Stockpiled topsoil or subsoil locations
X
N/A
_____ If the same person conducts the land-disturbing activity & any _____ Area & acreage to be stabilized with vegetation
X
related borrow or waste activity, the related borrow or waste _____ Method of soil preparation
X
activity shall constitute part of the land-disturbing activity unless _____ Seed type & rates (temporary & permanent)
X
the borrow or waste activity is regulated under the Mining Act of _____ Fertilizer type and rates
X
1971, or is a landfill regulated by the Division of Waste _____ Mulch type and rates (include mulch anchoring methods)
Management. If the land-disturbing activity and any related
borrow or waste activity are not conducted by the same person, NOTE: Plan should include provisions for groundcover in accordance with
they shall be considered separate land-disturbing activities and NPDES Construction Stormwater General Permit NCG010000.
must be permitted either through the Sedimentation Pollution
Control Act as a one-use borrow site or through the Mining Act. FINANCIAL RESPONSIBILITY/OWNERSHIP FORM
N/A
______ Location and details associated with any onsite stone crushing or
X
other processing of material excavated. If the affected area _____ Completed, signed & notarized FR/O Form
X
associated with excavation, processing, stockpiles and transport _____ Accurate application fee payable to NCDEQ ($65.00 per acre
of such materials will comprise 1 or more acres, and materials will rounded up the next acre with no ceiling amount)
X
be leaving the development tract, a mining permit will be required. _____ Certificate of assumed name, if the owner is a partnership
N/A
X
______ Required Army Corps 404 permit and Water Quality 401 _____ Name of Registered Agent (if applicable)
X
certification (e.g. stream disturbances over 150 linear feet) _____ Copy of the most current Deed for the site. Please make sure the
deed(s) and ownership information are consistent between the
EROSION & SEDIMENT CONTROL MEASURES (on plan) plan sheets, local records and this form.
X
_____ Provide latitude & longitude (in decimal degrees) at the project
X
______ Legend (provide appropriate symbols for all measures and entrance.
X
reference them to the construction details) _____ Two hard-copies of the plans (some regional offices require
X
______ Location of temporary measures additional plans or multiple sizes; please contact the regional
X
______ Location of permanent measures coordinator prior to such submittal.)
X
______ Construction drawings and details for
temporary and permanent measures. Show measures to scale on NOTE: For the Express Permitting Option, inquire at the local Regional
plan and include proposed contours where necessary. Ensure Office for availability. Express Reviews are performed by
design storage requirements are maintained through all phases of appointment only.
construction.
X
_____ Maintenance requirements for measures NARRATIVE AND CONSTRUCTION SEQUENCE
X
_____ Contact person responsible for maintenance
X
_____ Narrative describing the nature & purpose of the construction
SITE DRAINAGE FEATURES activity.
X
_____ Construction sequence related to erosion and sediment control
X
_____ Existing and planned drainage patterns (include off-site areas that (including installation of critical measures prior to the initiation of
drain through project and address temporary and permanent the land-disturbing activity & removal of measures after areas they
conveyance of stormwater over graded slopes) serve are permanently stabilized). Address all phases of
X
_____ Method used to determine acreage of land being disturbed and construction and necessary practices associated with temporary
drainage areas to all proposed measures (e.g. delineation map) stream bypasses and/or crossings.
XX
_____ Size, pipe material and location of culverts and sewers _____ Bid specifications related only to erosion control
X
_____ Soil information: type, special characteristics
X
_____ Soil information below culvert storm outlets rev. 05142019

Type II 24-hr 2-year, 24-hour Rainfall=3.61"
Hills Machinery Stormwater R3
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Summary for Subcatchment 1S: Pre Devolment Condition
Runoff=9.50 cfs @ 12.08 hrs, Volume=26,947 cf, Depth=1.95"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs
Type II 24-hr 2-year, 24-hour Rainfall=3.61"
Area (sf)CNDescription
165,70283Fallow, crop residue, Good, HSG B
165,702100.00% Pervious Area
TcLengthSlopeVelocityCapacityDescription
(min)(feet)(ft/ft)(ft/sec)(cfs)
15.43000.05000.32
Sheet Flow,
Grass: Short n= 0.150 P2= 3.61"

Type II 24-hr 2-year, 24-hour Rainfall=3.61"
Hills Machinery Stormwater R3
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Subcatchment 1S: Pre Devolment Condition
Hydrograph
Runoff
10
9.50 cfs
Type II 24-hr
9
2-year
8
24-hour Rainfall=3.61"
7
Runoff Area=165,702 sf
Runoff Volume=26,947 cf
6
Runoff Depth=1.95"
5
Flow (cfs)
Flow Length=300'
4
Slope=0.0500 '/'
3
Tc=15.4 min
CN=83
2
1
0
0123456789101112131415161718192021222324252627282930
Time (hours)

Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Hills Machinery Stormwater R3
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Summary for Subcatchment 1S: Pre Devolment Condition
Runoff=15.72 cfs @ 12.07 hrs, Volume=44,956 cf, Depth=3.26"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs
Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Area (sf)CNDescription
165,70283Fallow, crop residue, Good, HSG B
165,702100.00% Pervious Area
TcLengthSlopeVelocityCapacityDescription
(min)(feet)(ft/ft)(ft/sec)(cfs)
15.43000.05000.32
Sheet Flow,
Grass: Short n= 0.150 P2= 3.61"

Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Hills Machinery Stormwater R3
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Subcatchment 1S: Pre Devolment Condition
Hydrograph
Runoff
17
15.72 cfs
16
Type II 24-hr
15
10-year
14
13
24-hour Rainfall=5.09"
12
Runoff Area=165,702 sf
11
10 Runoff Volume=44,956 cf
9
Runoff Depth=3.26"
8
Flow (cfs)
Flow Length=300'
7
Slope=0.0500 '/'
6
5
Tc=15.4 min
4
CN=83
3
2
1
0
0123456789101112131415161718192021222324252627282930
Time (hours)

Type II 24-hr 25-year, 24-hour Rainfall=5.94"
Hills Machinery Stormwater R3
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Summary for Subcatchment 1S: Pre Devolment Condition
Runoff=19.35 cfs @ 12.07 hrs, Volume=55,727 cf, Depth=4.04"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs
Type II 24-hr 25-year, 24-hour Rainfall=5.94"
Area (sf)CNDescription
165,70283Fallow, crop residue, Good, HSG B
165,702100.00% Pervious Area
TcLengthSlopeVelocityCapacityDescription
(min)(feet)(ft/ft)(ft/sec)(cfs)
15.43000.05000.32
Sheet Flow,
Grass: Short n= 0.150 P2= 3.61"

Type II 24-hr 25-year, 24-hour Rainfall=5.94"
Hills Machinery Stormwater R3
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Subcatchment 1S: Pre Devolment Condition
Hydrograph
Runoff
21
19.35 cfs
20
19
Type II 24-hr
18
25-year
17
16
24-hour Rainfall=5.94"
15
Runoff Area=165,702 sf
14
13
Runoff Volume=55,727 cf
12
11
Runoff Depth=4.04"
10
Flow (cfs)
Flow Length=300'
9
8
Slope=0.0500 '/'
7
6
Tc=15.4 min
5
CN=83
4
3
2
1
0
0123456789101112131415161718192021222324252627282930
Time (hours)

Type II 24-hr WQ Rainfall=1.00"
Hills Machinery Stormwater R3
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Summary for Pond 9P: Bioretention
Inflow Area =165,715 sf,38.78% Impervious, Inflow Depth = 0.27" for WQ event
Inflow=1.71 cfs @ 11.93 hrs, Volume=3,793 cf
Outflow=0.24 cfs @ 12.22 hrs, Volume=3,793 cf, Atten= 86%, Lag= 17.6 min
Discarded=0.24 cfs @ 12.22 hrs, Volume=3,793 cf
Primary=0.00 cfs @ 0.00 hrs, Volume=0 cf
Secondary=0.00 cfs @ 0.00 hrs, Volume=0 cf
Routing by Dyn-Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs
Peak Elev= 2,166.19' @ 12.22 hrs Surf.Area= 5,173 sf Storage= 968 cf
Flood Elev= 2,170.00' Surf.Area= 9,176 sf Storage= 27,968 cf
Plug-Flow detention time= 24.6 min calculated for 3,792 cf (100% of inflow)
Center-of-Mass det. time= 24.6 min ( 864.3 - 839.7 )
VolumeInvertAvail.StorageStorage Description
#12,166.00'28,892 cf
50.00'W x 100.00'L x 4.10'H Prismatoid Z=3.0
DeviceRouting InvertOutlet Devices
#1Primary2,163.00'L= 175.0' Ke= 0.500
18.0" Round Culvert
Inlet / Outlet Invert= 2,163.00' / 2,160.50' S= 0.0143 '/' Cc= 0.900
n= 0.015 Concrete sewer w/manholes & inlets, Flow Area= 1.77 sf
#2Device 12,168.50' C= 0.600
48.0" x 48.0" Horiz. Orifice/Grate
Limited to weir flow at low heads
#3Discarded2,166.00'
2.000 in/hr Exfiltration over Surface area
Conductivity to Groundwater Elevation = 2,157.00' Phase-In= 0.01'
#4Secondary2,170.00'2 End Contraction(s)
10.0' long Sharp-Crested Rectangular Weir
1.0' Crest Height
Max=0.24 cfs @ 12.22 hrs HW=2,166.19' (Free Discharge)
Discarded OutFlow
( Controls 0.24 cfs)
3=Exfiltration
Max=0.00 cfs @ 0.00 hrs HW=2,166.00' (Free Discharge)
Primary OutFlow
(Passes 0.00 cfs of 11.82 cfs potential flow)
1=Culvert
( Controls 0.00 cfs)
2=Orifice/Grate
Max=0.00 cfs @ 0.00 hrs HW=2,166.00' (Free Discharge)
Secondary OutFlow
( Controls 0.00 cfs)
4=Sharp-Crested Rectangular Weir

Type II 24-hr WQ Rainfall=1.00"
Hills Machinery Stormwater R3
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Pond 9P: Bioretention
Hydrograph
Inflow
1.71 cfs
Outflow
Discarded
Inflow Area=165,715 sf
Primary
Secondary
Peak Elev=2,166.19'
Storage=968 cf
1
Flow (cfs)
0.24 cfs
0.24 cfs
0.00 cfs
0.00 cfs
0
0123456789101112131415161718192021222324252627282930
Time (hours)

Type II 24-hr 2-year, 24-hour Rainfall=3.61"
Hills Machinery Stormwater R3
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Summary for Pond 9P: Bioretention
Inflow Area =165,715 sf,38.78% Impervious, Inflow Depth = 2.31" for 2-year, 24-hour event
Inflow=15.73 cfs @ 11.93 hrs, Volume=31,844 cf
Outflow=1.08 cfs @ 12.52 hrs, Volume=29,204 cf, Atten= 93%, Lag= 35.5 min
Discarded=0.43 cfs @ 12.52 hrs, Volume=27,156 cf
Primary=0.65 cfs @ 12.52 hrs, Volume=2,048 cf
Secondary=0.00 cfs @ 0.00 hrs, Volume=0 cf
Routing by Dyn-Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs
Peak Elev= 2,168.55' @ 12.52 hrs Surf.Area= 7,533 sf Storage= 15,902 cf
Flood Elev= 2,170.00' Surf.Area= 9,176 sf Storage= 27,968 cf
Plug-Flow detention time= 361.5 min calculated for 29,194 cf (92% of inflow)
Center-of-Mass det. time= 317.0 min ( 1,115.6 - 798.6 )
VolumeInvertAvail.StorageStorage Description
#12,166.00'28,892 cf
50.00'W x 100.00'L x 4.10'H Prismatoid Z=3.0
DeviceRouting InvertOutlet Devices
#1Primary2,163.00'L= 175.0' Ke= 0.500
18.0" Round Culvert
Inlet / Outlet Invert= 2,163.00' / 2,160.50' S= 0.0143 '/' Cc= 0.900
n= 0.015 Concrete sewer w/manholes & inlets, Flow Area= 1.77 sf
#2Device 12,168.50' C= 0.600
48.0" x 48.0" Horiz. Orifice/Grate
Limited to weir flow at low heads
#3Discarded2,166.00'
2.000 in/hr Exfiltration over Surface area
Conductivity to Groundwater Elevation = 2,157.00' Phase-In= 0.01'
#4Secondary2,170.00'2 End Contraction(s)
10.0' long Sharp-Crested Rectangular Weir
1.0' Crest Height
Max=0.43 cfs @ 12.52 hrs HW=2,168.55' (Free Discharge)
Discarded OutFlow
( Controls 0.43 cfs)
3=Exfiltration
Max=0.65 cfs @ 12.52 hrs HW=2,168.55' (Free Discharge)
Primary OutFlow
(Passes 0.65 cfs of 15.13 cfs potential flow)
1=Culvert
(Weir Controls 0.65 cfs @ 0.76 fps)
2=Orifice/Grate
Max=0.00 cfs @ 0.00 hrs HW=2,166.00' (Free Discharge)
Secondary OutFlow
( Controls 0.00 cfs)
4=Sharp-Crested Rectangular Weir

Type II 24-hr 2-year, 24-hour Rainfall=3.61"
Hills Machinery Stormwater R3
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Pond 9P: Bioretention
Hydrograph
Inflow
15.73 cfs
Outflow
Discarded
Inflow Area=165,715 sf
Primary
Secondary
Peak Elev=2,168.55'
17
16
Storage=15,902 cf
15
14
13
12
11
10
9
8
Flow (cfs)
7
6
5
1.08 cfs
4
0.43 cfs
3
0.65 cfs
2
0.00 cfs 1
0
0123456789101112131415161718192021222324252627282930
Time (hours)

Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Hills Machinery Stormwater R3
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Summary for Pond 9P: Bioretention
Inflow Area =165,715 sf,38.78% Impervious, Inflow Depth = 3.66" for 10-year, 24-hour event
Inflow=24.58 cfs @ 11.93 hrs, Volume=50,575 cf
Outflow=16.08 cfs @ 11.99 hrs, Volume=46,067 cf, Atten= 35%, Lag= 3.9 min
Discarded=0.46 cfs @ 11.99 hrs, Volume=29,892 cf
Primary=15.61 cfs @ 11.99 hrs, Volume=16,175 cf
Secondary=0.00 cfs @ 0.00 hrs, Volume=0 cf
Routing by Dyn-Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs
Peak Elev= 2,168.95' @ 11.99 hrs Surf.Area= 7,970 sf Storage= 18,986 cf
Flood Elev= 2,170.00' Surf.Area= 9,176 sf Storage= 27,968 cf
Plug-Flow detention time= 247.6 min calculated for 46,051 cf (91% of inflow)
Center-of-Mass det. time= 200.5 min ( 988.5 - 788.0 )
VolumeInvertAvail.StorageStorage Description
#12,166.00'28,892 cf
50.00'W x 100.00'L x 4.10'H Prismatoid Z=3.0
DeviceRouting InvertOutlet Devices
#1Primary2,163.00'L= 175.0' Ke= 0.500
18.0" Round Culvert
Inlet / Outlet Invert= 2,163.00' / 2,160.50' S= 0.0143 '/' Cc= 0.900
n= 0.015 Concrete sewer w/manholes & inlets, Flow Area= 1.77 sf
#2Device 12,168.50' C= 0.600
48.0" x 48.0" Horiz. Orifice/Grate
Limited to weir flow at low heads
#3Discarded2,166.00'
2.000 in/hr Exfiltration over Surface area
Conductivity to Groundwater Elevation = 2,157.00' Phase-In= 0.01'
#4Secondary2,170.00'2 End Contraction(s)
10.0' long Sharp-Crested Rectangular Weir
1.0' Crest Height
Max=0.46 cfs @ 11.99 hrs HW=2,168.95' (Free Discharge)
Discarded OutFlow
( Controls 0.46 cfs)
3=Exfiltration
Max=15.58 cfs @ 11.99 hrs HW=2,168.95' (Free Discharge)
Primary OutFlow
(Barrel Controls 15.58 cfs @ 8.81 fps)
1=Culvert
(Passes 15.58 cfs of 15.81 cfs potential flow)
2=Orifice/Grate
Max=0.00 cfs @ 0.00 hrs HW=2,166.00' (Free Discharge)
Secondary OutFlow
( Controls 0.00 cfs)
4=Sharp-Crested Rectangular Weir

Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Hills Machinery Stormwater R3
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Pond 9P: Bioretention
Hydrograph
Inflow
24.58 cfs
Outflow
Discarded
Inflow Area=165,715 sf
Primary
Secondary
Peak Elev=2,168.95'
26
Storage=18,986 cf
24
22
16.08 cfs
20
15.61 cfs
18
16
14
12
Flow (cfs)
10
8
6
0.46 cfs
4
2
0.00 cfs
0
0123456789101112131415161718192021222324252627282930
Time (hours)

Type II 24-hr 25-year, 24-hour Rainfall=5.94"
Hills Machinery Stormwater R3
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Summary for Pond 9P: Bioretention
Inflow Area =165,715 sf,38.78% Impervious, Inflow Depth = 4.46" for 25-year, 24-hour event
Inflow=29.69 cfs @ 11.93 hrs, Volume=61,640 cf
Outflow=16.46 cfs @ 12.01 hrs, Volume=56,294 cf, Atten= 45%, Lag= 4.5 min
Discarded=0.50 cfs @ 12.01 hrs, Volume=31,150 cf
Primary=15.97 cfs @ 12.01 hrs, Volume=25,144 cf
Secondary=0.00 cfs @ 0.00 hrs, Volume=0 cf
Routing by Dyn-Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs
Peak Elev= 2,169.30' @ 12.01 hrs Surf.Area= 8,364 sf Storage= 21,849 cf
Flood Elev= 2,170.00' Surf.Area= 9,176 sf Storage= 27,968 cf
Plug-Flow detention time= 209.8 min calculated for 56,276 cf (91% of inflow)
Center-of-Mass det. time= 163.7 min ( 947.1 - 783.4 )
VolumeInvertAvail.StorageStorage Description
#12,166.00'28,892 cf
50.00'W x 100.00'L x 4.10'H Prismatoid Z=3.0
DeviceRouting InvertOutlet Devices
#1Primary2,163.00'L= 175.0' Ke= 0.500
18.0" Round Culvert
Inlet / Outlet Invert= 2,163.00' / 2,160.50' S= 0.0143 '/' Cc= 0.900
n= 0.015 Concrete sewer w/manholes & inlets, Flow Area= 1.77 sf
#2Device 12,168.50' C= 0.600
48.0" x 48.0" Horiz. Orifice/Grate
Limited to weir flow at low heads
#3Discarded2,166.00'
2.000 in/hr Exfiltration over Surface area
Conductivity to Groundwater Elevation = 2,157.00' Phase-In= 0.01'
#4Secondary2,170.00'2 End Contraction(s)
10.0' long Sharp-Crested Rectangular Weir
1.0' Crest Height
Max=0.50 cfs @ 12.01 hrs HW=2,169.30' (Free Discharge)
Discarded OutFlow
( Controls 0.50 cfs)
3=Exfiltration
Max=15.96 cfs @ 12.01 hrs HW=2,169.30' (Free Discharge)
Primary OutFlow
(Barrel Controls 15.96 cfs @ 9.03 fps)
1=Culvert
(Passes 15.96 cfs of 37.48 cfs potential flow)
2=Orifice/Grate
Max=0.00 cfs @ 0.00 hrs HW=2,166.00' (Free Discharge)
Secondary OutFlow
( Controls 0.00 cfs)
4=Sharp-Crested Rectangular Weir

Type II 24-hr 25-year, 24-hour Rainfall=5.94"
Hills Machinery Stormwater R3
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Pond 9P: Bioretention
Hydrograph
Inflow
29.69 cfs
Outflow
Discarded
Inflow Area=165,715 sf
Primary
Secondary
Peak Elev=2,169.30'
32
30
Storage=21,849 cf
28
26
24
16.46 cfs
22
20
15.97 cfs
18
16
14
Flow (cfs)
12
10
8
6
0.50 cfs
4
2
0.00 cfs
0
0123456789101112131415161718192021222324252627282930
Time (hours)

Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Hills Machinery Stormwater R3
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Summary for Subcatchment 2S: Hills Machinery Sub Area
Runoff=4.99 cfs @ 11.94 hrs, Volume=9,709 cf, Depth=3.65"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs
Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Area (sf)CNDescription
*10,40098B11 Hills Roof
*2,50098B14 Wash Pit Roof
*9,20098B2 Concrete Parking
9,80061>75% Grass cover, Good, HSG B
31,90087Weighted Average
9,80030.72% Pervious Area
22,10069.28% Impervious Area
TcLengthSlopeVelocityCapacityDescription
(min)(feet)(ft/ft)(ft/sec)(cfs)
3.32400.00831.22
Sheet Flow, Hills Machinery Sub Tc
Smooth surfaces n= 0.011 P2= 3.61"

Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Hills Machinery Stormwater R3
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Summary for Subcatchment 4S: Lease Space 1 Sub Basin
Runoff=3.85 cfs @ 11.92 hrs, Volume=6,926 cf, Depth=3.06"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs
Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Area (sf)CNDescription
*10,40098Roof
*3,91798Concrete Parking
12,80061>75% Grass cover, Good, HSG B
27,11781Weighted Average
12,80047.20% Pervious Area
14,31752.80% Impervious Area
TcLengthSlopeVelocityCapacityDescription
(min)(feet)(ft/ft)(ft/sec)(cfs)
2.01210.00701.00
Sheet Flow, Flow to SG3
Smooth surfaces n= 0.011 P2= 3.61"

Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Hills Machinery Stormwater R3
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Summary for Subcatchment 12S: Main Gravel Area
Runoff=10.59 cfs @ 11.95 hrs, Volume=21,107 cf, Depth=3.45"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs
Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Area (sf)CNDescription
*73,38885B8 Gravel Parking
73,388100.00% Pervious Area
TcLengthSlopeVelocityCapacityDescription
(min)(feet)(ft/ft)(ft/sec)(cfs)
4.42400.00400.91
Sheet Flow, Gravel parking area
Smooth surfaces n= 0.011 P2= 3.61"

Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Hills Machinery Stormwater R3
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Summary for Subcatchment 13S: Lease 2 Future Gravel
\[49\] Hint: Tc<2dt may require smaller dt
Runoff=0.88 cfs @ 11.91 hrs, Volume=1,570 cf, Depth=3.45"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs
Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Area (sf)CNDescription
*5,46085B9 Gravel
5,460100.00% Pervious Area
TcLengthSlopeVelocityCapacityDescription
(min)(feet)(ft/ft)(ft/sec)(cfs)
1.01200.04202.04
Sheet Flow, Overland gravel
Smooth surfaces n= 0.011 P2= 3.61"

Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Hills Machinery Stormwater R3
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Summary for Subcatchment 10S: Lease Space 2
\[49\] Hint: Tc<2dt may require smaller dt
Runoff=2.70 cfs @ 11.91 hrs, Volume=5,632 cf, Depth=4.85"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs
Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Area (sf)CNDescription
*10,40098B13 Roof
*3,52598B4 Concrete Parking
13,92598Weighted Average
13,925100.00% Impervious Area
TcLengthSlopeVelocityCapacityDescription
(min)(feet)(ft/ft)(ft/sec)(cfs)
1.01200.04202.04
Sheet Flow,
Smooth surfaces n= 0.011 P2= 3.61"

Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Hills Machinery Stormwater R3
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Summary for Subcatchment 6S: Future Building
Runoff=2.65 cfs @ 11.92 hrs, Volume=5,632 cf, Depth=4.85"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs
Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Area (sf)CNDescription
*10,40098B10 Roof
*3,52598B1 Parking
13,92598Weighted Average
13,925100.00% Impervious Area
TcLengthSlopeVelocityCapacityDescription
(min)(feet)(ft/ft)(ft/sec)(cfs)
1.61250.01401.32
Sheet Flow, Tc Future Building
Smooth surfaces n= 0.011 P2= 3.61"

Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Hills Machinery Stormwater R3
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Summary for Pond 3P: Pipes 1,2,5,6
Inflow Area =31,900 sf,69.28% Impervious, Inflow Depth = 3.65" for 10-year, 24-hour event
Inflow=4.99 cfs @ 11.94 hrs, Volume=9,709 cf
Outflow=4.99 cfs @ 11.94 hrs, Volume=9,709 cf, Atten= 0%, Lag= 0.0 min
Primary=4.99 cfs @ 11.94 hrs, Volume=9,709 cf
Routing by Dyn-Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs
Peak Elev= 2,171.55' @ 11.94 hrs
Flood Elev= 2,177.00'
DeviceRouting InvertOutlet Devices
#1Primary2,170.00'
18.0" Round P2 18" RCP
L= 290.0' CMP, square edge headwall, Ke= 0.500
Inlet / Outlet Invert= 2,170.00' / 2,169.60' S= 0.0014 '/' Cc= 0.900
n= 0.011 Concrete pipe, straight & clean, Flow Area= 1.77 sf
Max=4.98 cfs @ 11.94 hrs HW=2,171.55' TW=2,170.69' (Dynamic Tailwater)
Primary OutFlow
(Barrel Controls 4.98 cfs @ 3.38 fps)
1=P2 18" RCP

Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Hills Machinery Stormwater R3
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Summary for Pond 7P: Pipe 4 18"RCP
Inflow Area =13,925 sf,100.00% Impervious, Inflow Depth = 4.85" for 10-year, 24-hour event
Inflow=2.65 cfs @ 11.92 hrs, Volume=5,632 cf
Outflow=2.65 cfs @ 11.92 hrs, Volume=5,632 cf, Atten= 0%, Lag= 0.0 min
Primary=2.65 cfs @ 11.92 hrs, Volume=5,632 cf
Routing by Dyn-Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs
Peak Elev= 2,173.26' @ 11.92 hrs
Flood Elev= 2,177.50'
DeviceRouting InvertOutlet Devices
#1Primary2,172.50'
18.0" Round 18" RCP
L= 121.0' RCP, square edge headwall, Ke= 0.500
Inlet / Outlet Invert= 2,172.50' / 2,169.60' S= 0.0240 '/' Cc= 0.900
n= 0.015 Concrete sewer w/manholes & inlets, Flow Area= 1.77 sf
Max=2.64 cfs @ 11.92 hrs HW=2,173.26' TW=2,170.70' (Dynamic Tailwater)
Primary OutFlow
(Inlet Controls 2.64 cfs @ 2.96 fps)
1=18" RCP

Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Hills Machinery Stormwater R3
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Summary for Pond 5P: Pipe 7 18"RCP
Inflow Area =27,117 sf,52.80% Impervious, Inflow Depth = 3.06" for 10-year, 24-hour event
Inflow=3.85 cfs @ 11.92 hrs, Volume=6,926 cf
Outflow=3.85 cfs @ 11.92 hrs, Volume=6,926 cf, Atten= 0%, Lag= 0.0 min
Primary=3.85 cfs @ 11.92 hrs, Volume=6,926 cf
Routing by Dyn-Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs
Peak Elev= 2,171.85' @ 11.93 hrs
Flood Elev= 2,176.00'
DeviceRouting InvertOutlet Devices
#1Primary2,170.80'
18.0" Round Pipe 7 18" RCP
L= 121.0' RCP, square edge headwall, Ke= 0.500
Inlet / Outlet Invert= 2,170.80' / 2,169.60' S= 0.0099 '/' Cc= 0.900
n= 0.015 Concrete sewer w/manholes & inlets, Flow Area= 1.77 sf
Max=3.79 cfs @ 11.92 hrs HW=2,171.84' TW=2,170.72' (Dynamic Tailwater)
Primary OutFlow
(Outlet Controls 3.79 cfs @ 4.08 fps)
1=Pipe 7 18" RCP

Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Hills Machinery Stormwater R3
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Summary for Pond 8P: Pipe 3 24" RCP
Inflow Area =72,942 sf,69.02% Impervious, Inflow Depth = 3.66" for 10-year, 24-hour event
Inflow=11.33 cfs @ 11.93 hrs, Volume=22,266 cf
Outflow=11.33 cfs @ 11.93 hrs, Volume=22,266 cf, Atten= 0%, Lag= 0.0 min
Primary=11.33 cfs @ 11.93 hrs, Volume=22,266 cf
Routing by Dyn-Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs
Peak Elev= 2,170.72' @ 11.93 hrs
Flood Elev= 2,175.00'
DeviceRouting InvertOutlet Devices
#1Primary2,168.90'L= 203.0' Ke= 0.500
24.0" Round 24" RCP
Inlet / Outlet Invert= 2,168.90' / 2,167.75' S= 0.0057 '/' Cc= 0.900
n= 0.015 Concrete sewer w/manholes & inlets, Flow Area= 3.14 sf
Max=11.29 cfs @ 11.93 hrs HW=2,170.72' TW=2,168.64' (Dynamic Tailwater)
Primary OutFlow
(Barrel Controls 11.29 cfs @ 4.95 fps)
1=24" RCP

Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Hills Erosion Flow
Printed 9/25/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Summary for Subcatchment 1S: Cut Condition
\[49\] Hint: Tc<2dt may require smaller dt
Runoff=14.20 cfs @ 12.05 hrs, Volume=1.554 af, Depth=3.16"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 2.00-26.00 hrs, dt= 0.50 hrs
Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Area (ac)CNDescription
*5.90082Cut condition, dirt HSG B
5.900100.00% Pervious Area
TcLengthSlopeVelocityCapacityDescription
(min)(feet)(ft/ft)(ft/sec)(cfs)
17.13000.05000.29
Sheet Flow, Cut condition
Cultivated: Residue>20% n= 0.170 P2= 3.57"

Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Hills Erosion Flow
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Summary for Reach 6R: Skimmer Ditch
Inflow Area =3.300 ac,0.00% Impervious, Inflow Depth = 3.16" for 10-year, 24-hour event
Inflow=8.77 cfs @ 12.00 hrs, Volume=0.869 af
Outflow=8.11 cfs @ 12.01 hrs, Volume=0.874 af, Atten= 8%, Lag= 1.1 min
Routing by Stor-Ind+Trans method, Time Span= 2.00-26.00 hrs, dt= 0.50 hrs / 3
Max. Velocity= 4.38 fps, Min. Travel Time= 1.5 min
Avg. Velocity = 1.48 fps, Avg. Travel Time= 4.5 min
Peak Storage= 772 cf @ 12.01 hrs
Average Depth at Peak Storage= 0.54' , Surface Width= 5.21'
Bank-Full Depth= 1.50' Flow Area= 9.8 sf, Capacity= 75.84 cfs
2.00' x 1.50' deep channel, n= 0.022 Earth, clean & straight
Side Slope Z-value= 3.0 '/' Top Width= 11.00'
Length= 400.0' Slope= 0.0165 '/'
Inlet Invert= 2,173.90', Outlet Invert= 2,167.30'
Þ

Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Hills Erosion Flow
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Summary for Reach 7R: Trap 1 Ditch
Inflow Area =1.500 ac,0.00% Impervious, Inflow Depth = 3.16" for 10-year, 24-hour event
Inflow=3.92 cfs @ 11.99 hrs, Volume=0.395 af
Outflow=3.80 cfs @ 12.00 hrs, Volume=0.396 af, Atten= 3%, Lag= 0.5 min
Routing by Stor-Ind+Trans method, Time Span= 2.00-26.00 hrs, dt= 0.50 hrs / 3
Max. Velocity= 4.05 fps, Min. Travel Time= 0.6 min
Avg. Velocity = 1.35 fps, Avg. Travel Time= 1.8 min
Peak Storage= 135 cf @ 11.99 hrs
Average Depth at Peak Storage= 0.32' , Surface Width= 3.93'
Bank-Full Depth= 1.50' Flow Area= 9.8 sf, Capacity= 92.69 cfs
2.00' x 1.50' deep channel, n= 0.022 Earth, clean & straight
Side Slope Z-value= 3.0 '/' Top Width= 11.00'
Length= 142.0' Slope= 0.0246 '/'
Inlet Invert= 2,172.50', Outlet Invert= 2,169.00'
Þ

Type II 24-hr 10-year, 24-hour Rainfall=5.09"
Hills Erosion Flow
Printed 9/23/2020
Prepared by HP
HydroCAD® 10.10-3a s/n 11211 © 2020 HydroCAD Software Solutions LLC
Summary for Reach 9R: Trap 2 Ditch
Inflow Area =1.510 ac,0.00% Impervious, Inflow Depth = 3.16" for 10-year, 24-hour event
Inflow=3.95 cfs @ 11.99 hrs, Volume=0.398 af
Outflow=3.77 cfs @ 12.00 hrs, Volume=0.399 af, Atten= 5%, Lag= 0.7 min
Routing by Stor-Ind+Trans method, Time Span= 2.00-26.00 hrs, dt= 0.50 hrs / 3
Max. Velocity= 5.25 fps, Min. Travel Time= 0.9 min
Avg. Velocity = 1.73 fps, Avg. Travel Time= 2.7 min
Peak Storage= 206 cf @ 12.00 hrs
Average Depth at Peak Storage= 0.26' , Surface Width= 3.58'
Bank-Full Depth= 1.50' Flow Area= 9.8 sf, Capacity= 134.11 cfs
2.00' x 1.50' deep channel, n= 0.022 Earth, clean & straight
Side Slope Z-value= 3.0 '/' Top Width= 11.00'
Length= 281.0' Slope= 0.0516 '/'
Inlet Invert= 2,170.50', Outlet Invert= 2,156.00'
Þ

)/n
2/3
target valuetarget value
for (A*R
difference from
difference from
)/n)/n
2/32/3
1.936ft0.968ft2.000ft1.000ft
)/n
143.816 = target value
(A*R(A*R
2/3
= =
) =
DD
) = (A*R
=
1/2
=
r
1/2

r
nP, ftnP, ft
Calculations Pipe Diameter, Pipe Radius, Q/(1.49*S Q/(1.49*SPipe Diameter, Pipe radius,
2 2
in
15cfs 24
0.80
0.01123.23in
0.0049ft/ftThe Manning equation can be rearranged to:
, radiansA, ft, radiansA, ft
=
=
=
full
1
=
n
Q
y/D
=
=std
S
Enter values in blue boxes. Spreadsheet calculates values in yellow boxes DD

:
1.5490.391.8552.5250.01234.29143.8160.0000
flow depth, y ,fth, ft
flow depth, y ,fth, ft
Partially Full Pipe Flow Calculations - U.S. Units
Calculation of Required Diameter for the Pipe
InstructionsInputs
This spreadsheet will calculate the diameter needed for a target fraction full (y/D) for the pipe. Design Flow Rate, Manning Roughness, Slope of Pipe, Target Depth Fract.,
Pipe Diameter, (enter initial estimate)NOTE: You must use Excel's "Goal Seek" to find the pipe diameter as follows: Place the cursoron cell I 25 and click on "goal seek" (in
the "tools" menu of older versions and under "Data - WhatIf Analysis" in newer versions of Excel). Enter values to "Set cell:" I25, "To value:" 0, "Bychanging cell:" C17, and click
on "OK". The calculated value of D will appear in cell C17.The value of D calculated in cell C17 will almost certainly not be a standard pipe diameter. Enterthe next larger standard
pipe diameter in blue cell C32, an initial estimate for y in blue cell A36, andthe spreadsheet will calculate the values in the the yellow cells. You will need to use "goal seek"to
set cell I38 to 0 by changing cell A38, as described above. Next Larger Standard Pipe Diameter, Initial Estimate

4.775ft/sec
=
V
Ave. Velocity,
73.3%
)*100%\] =
full
0.632.3752.3010.01303.91124.640-19.1755
/A
http://www.engineeringtoolbox.com/nps-nominal-pipe-sizes-d_45.html
flow
A
1.374
pipe % full \[(Nominal diameters for standard U.S. pipe sizes ranging from 1/8 inch to 60 inches:1/8, 1/4, 3/8, 1/2, 3/4, 1, 1 1/4, 1 1/2, 2, 2 1/2, 3, 4, 6, 8,
10, 12, 14, 16, 18, 20, 22, 24, 26,28, 30, 32, 36, 40, 42, 44, 48, 52, 56, 60 Source:

2012
1.20
- (y/D)
0.54
(Manning Equation)
= 1 + (y/D)
full
n/n
)
:
1/2
full
)(S
2/3
Equations used for calculations - Less than Half Full: Equations used for calculations - More than half full:r = D/2 r = D/2h = y h = 2r - y
R = A/P(hydraulic radius)Q = (1.49/n)(A)(R
Equation used for n/n Source: Goswami, I., Civil Engineerign All-In-One PE Exam Guide: Beadth and Depth, 2nd Ed. (Eqn 303.32), McGraw-Hill, NY, NY,

M OUNTAIN S OILS, I NCORPORATED
15 Lone Coyote RidgeFletcher, NC 28732
Email: [e-mail] Cell: [phone]
Stormwater Infiltration Basin Evaluation

5745 Old Haywood Road
Parcel ID# 9632-47-9133 (12.08-Acres)
Henderson County, NC

Prepared for:

Tyson Griswold, P.E
Civil and Environmental Engineer
www.tysongriswold.com
[e-mail]
Phone: [phone]

Prepared by:
Mountain Soils, Inc.
15 Lone Coyote Ridge
Fletcher, North Carolina 28732

Steven J. Melin, LSS

August 12, 2020

Stormwater Infiltration Basin Evaluation - 5745 Old Haywood Road
Henderson County, North Carolina
INTRODUCTION

In August 2020, Mountain Soils, Inc. (MSI) investigated the proposed stormwater infiltration
area at 5745 Old Haywood Road for . The investigation was performed to
estimate the permeability of the soil material and to identify the depth to seasonal high water
table (if present). The investigation was performed using back-hoe pits. Additionally the
investigation used a Trimble Geo XT GPS unit (capable of sub-meter accuracy) to determine
locations evaluated at the site.

PRIMARY INVESTIGATORS' CREDENTIALS

Steve Melin: N.C. Licensed Soil Scientist (Certification # 1254)

Education: M.S. Natural Resource Administration - Soil Science Emphasis, North
Carolina State University; Raleigh, NC

B.S. Watershed Management, Soil Science Minor, University of Wisconsin-
Stevens Point, Stevens Point, WI

SITE FEATURES / SITE INVESTIGATION METHODS

th
The field evaluations were conducted on August 7, 2020. The soil material was evaluated by
excavated soil pits. The proposed stormwater infiltration basin areas were investigated by
making observations of the soil properties (depth, texture, structure, seasonal wetness, restrictive
horizons, etc.) to a depth of 72 inches (6 feet) when possible. Soil color was determined with a
Munsell Soil Color Chart.

The pits (P1 P4) in the proposed basin area reveal a layer of clay loam soil typically from 10-
24 deep
saprolite has a sandy loam texture with some rock fragments (>10%). A friable, slightly sticky,
slightly plastic consistency is noted. Also, there were no indications of a seasonal high water
table in the pits evaluated in the proposed stormwater basin.

Please note that the soils / saprolite encountered is consistent with the soil series mapped in the
area by the NRCS (USDA) Soils Map. This soil series (Hayesville sandy loam) is very deep,
well drained, and moderately permeable. Typically this soil formed in residuum weathered from
igneous and high-grade metamorphic rocks (i.e. gneiss parent material (granite / mica gneiss)).

The NRCS describes the Hayesville soil series as well drained; moderate permeability in the
subsoil and moderately rapid permeability in the underlying material. Please note that moderate
permeability is defined by NRCS as a value between 2.0 to 6.0 inches per hour (moderate
permeability has a range between 0.60 and 2.0 inches per hour).

August 2020
2

Stormwater Infiltration Basin Evaluation - 5745 Old Haywood Road
Henderson County, North Carolina
CONCLUSIONS / RECOMMENDATIONS

The soil evaluation process revealed that soils are relatively uniform and homogenous
throughout the proposed basin area. The evaluations indicate that the soil/saprolite material
moves water and there is not a seasonal high water table noted in the pits in the stormwater basin
area.

evaluation. We appreciate the opportunity to provide with you with our services. Please do not
hesitate to contact us if you have any questions. Thanks

Best Regards,

Steven J. Melin, LSS
August 2020
3

Soils and Stormwater Evaluation. Hills Machinery - 5475 Old Haywood Road. PIN# 9632-47-9133; Mills River; Henderson Co., NC (MSI (August 2020))
Potential Well
#
100' Well Setback
Pit
"
Auger Boring
·
GPS Points - May
GPS Points - August
Proposed Driveway
Powerline ROW
Powerline
Initial Drainline - Pink Pin Flags
Repair Area
Septic Tank
A2
Stormwater Basin
A1
Approximate Boundary
A3
A5
P2
"
P1
"
4 Pits Evaluated
P4
P3
"
"
A4
rky
Illustrative maps generated are for soil information and onsite wastewater
data only. Maps generated are not surveys and any level of accuracy is
not claimed. All locations are approximate; this map is not a survey.
1 inch = 120 feet
Illustrative maps produced cannot be used as legal documentation for land
transfers or other situations that require a legally surveyed boundary. The
map was generated from survey marks, as well as GPS Points, aerial
0120240480
photography from NC OneMap, and Henderson County GIS data.
Feet

Soils and Stormwater Evaluation. Hills Machinery - 5475 Old Haywood Road. PIN# 9632-47-9133; Mills River; Henderson Co., NC (MSI (August 2020))
Potential Well
#
100' Well Setback
Pit
"
Auger Boring
·
GPS Points - May
GPS Points - August
Proposed Driveway
Powerline ROW
Powerline
Initial Drainline - Pink Pin Flags
Repair Area
Septic Tank
A2
Stormwater Basin
A1
Approximate Boundary
A3
A5
P2
"
P1
"
4 Pits Evaluated
P4
P3
"
"
A4
rky
Illustrative maps generated are for soil information and onsite wastewater
data only. Maps generated are not surveys and any level of accuracy is
not claimed. All locations are approximate; this map is not a survey.
1 inch = 120 feet
Illustrative maps produced cannot be used as legal documentation for land
transfers or other situations that require a legally surveyed boundary. The
map was generated from survey marks, as well as GPS Points, aerial
0120240480
photography from NC OneMap, and Henderson County GIS data.
Feet