HomeMy WebLinkAboutKewaunee Scientific - 01-Stormwater Report 2 110518
November 5, 2018
Mr. Corey Anen
Environmental Engineer
NCDEQ-DEMLR
1612 Mail Service Center
Raleigh, NC 27699-1612
Subject: Submittal 2
Stormwater Permit No. SW3180903
Kewaunee Scientific – Statesville, NC
Iredell County
Dear Mr. Anen:
The following items have been addressed in accordance with your review letter dated October 29, 2018:
1. Electronic copy of plan set has been uploaded.
2. Sediment storage depth (1 ft) was excluded when calculating forebay volume.
3. Rainfall amount was adjusted from 1.4 inches to 1.0 inches.
4. The calculations were adjusted to use equation 2 to calaculate average depth.
5. All general MDC’s and how they were addressed was added to the report. A maintenance
easement was added to the site plan and grading plan, and once record drawings are complete,
the easement will be platted and recorded dedicating the easement to NCDEQ-DEMLR.
6. Supplement EZ Form is included with this submittal
7. Per our conversation, digital files will be included, some as Excel files, not .pdf files.
Please let me know if you need any additional information, or if you have any questions regarding
submittal #2..
Regards,
P. Scott Bell, PE
Senior Engineer
G.L. Wilson Building Co, Inc.
STORMWATER MANAGEMENT
REPORT
PREPARED FOR
Kewaunee Warehouse Expansion
SW3180903
2340 W. Front St.
Statesville, NC
November 5, 2018
By:
P. Scott Bell, PE
PROJECT NARRATIVE:
The site is located on the North side of W. Front Street, between Autec and Mt. Aire
Farms properties in West Statesville. The southern boundary is W. Front Street, and the
northern side of the site is bounded by Alexander RY rail site. Site soils are Urban Land
based on mapping from NRCS - Iredell. The site is predominantly developed, with a
berm along the railway right of way. This phase of development will be complete build
out for this parcel. The site currently has a 100,000 SF warehouse, associated docks
and parking as shown on existing conditions sheet C0.1. There is also an existing dry
detention pond between the building and W. Front Street. Design parameters for outlet
structure are shown on the existing conditions plan as well
Existing utilities (water, sewer, electricity, gas) are available onsite.
The storm drainage calculations are based on the rational method. Drainage area maps
for the pre-developed and post-developed conditions are attached (sheets D-1and D-2).
Following each map is a data table used to calculate the composite CN, and composite
rational “C” values. Calculations for peak discharge were determined using an excel
spreadsheet. These flow rates were then used in Carlson Hydraulic modeling software
to determine culvert size based on flowing 50% full during a 10 year storm event.
Permanent storm water quantity is being provided on this site by converting the dry
pond and existing outlet structure to a wet pond. Calculations for design are included
with this submittal. The proposed system attenuates the post-developed flows for the 1
year, 2 year, and 10 year storm events (see page 2 of the Hydraflow calculations for a
summary).
The site slopes from north to south, toward the existing dry pond. Earthworks for the site
will require export of structural fill and topsoil. Some topsoil from this site will be used on
fill and cut slopes to insure that vegetation is established promptly after work is
complete, excess will be transported to a nearby site, to be permitted separately, but
concurrently with this submittal.
Stormwater runoff shall be collected by use of swales, drainage piping, temporary slope
drains, catch basins, and ADS Nyoplast inlets. The storm drainage is designed for a 10-
year storm frequency. Silt fence, straw wattles, and sediment fence rock outlets will be
constructed and maintained in accordance with the plans and project details.
Erosion Control Plan has been to Iredell County Development Services, Planning
Division – Erosion Control Section on August 30, 2018.
Table of Contents 1:
USGS Quad, Statesville West EX-A
Pre-developed Drainage Area Map D-1
Pre-developed Composite CN 2
Post-developed Drainage Area Map D-2
Post-developed Composite CN 3
MDC Investigation 4
Current Deed 10
Deed Restrictions 13
Secretary of State LP filing 15
Storm EZ Application 17
Attachments:
Hydraflow pre-developed hydraulic analysis
Hydraflow post-developed hydraulic analysis
USGS Quad, Statesville West,
Exhibit A
MDC Investigation:
STORAGE VOLUME
CALCULATIONS
Drainage Area: 9.98 Ac.
Runoff Depth (Rd): 1.0 inch
RUNOFF VOLUME TO
TREAT:
Rv=0.05+0.9Ia
Pre-Development Area:
Impervious 3.6 Ac.
Gravel 1.97 Ac.
Grass: 4.41 Ac.
Woods: 0 Ac.
Total: 9.98 Ac.
Post-Development
Area:
Impervious 5.39 Ac.
Gravel 1.41 Ac.
Grass: 3.18 Ac.
Woods: Ac.
Total: 9.98 Ac.
Ia: 0.681
Rv= 0.663
Volume to Treat:
Minimum Temporary
Pool Volume
V=3630xRdxRvxA
V= 24,027 C.F.
Volume provided 29,450 cf (elev.= 951.50)
Permanent Pool Calculations
Pool Forebay1 Forebay 2 Pool Pool
Area Area Area inc vol cum vol
946 0 0 0
947 3098 0 0 0 0
948 4142 285 0 3620 3620
949 5288 556 0 4715 8335
950 6445 897 253 5866.5 14201.5
951 7658 1295 485 7051.5 21253
951.5 9817 1517 602 8197.75 29450.75
952 14778 11057.25 40508
Vpp = 29450.75
App= 9817
Davg= 3.00
} 1 ft sediment storage
Minimum sediment storage in main pool and forebays is 1 ft
Pond has 2 forebays (hence, 2 inlets), and the outlet structure is placed midway
between the two inlets.
Elev Forebay1 Forebay1 Forebay 2 Forebay 2
Area inc vol cum vol Area inc vol cum vol
946 0 0 0 0 0 0
947 0 0 0
0 0 0
948 285 0 0 0 0 0
949 556 420.5 420.5 0 0 0
950 897 726.5 1147 253 0 0
951 1295 1096 2243 485 369 369
951.5 1517 1406 3649 602 543.5 912.5
Vol. Main Pool= 29450.75
Volume Forebays= 4561.5
15% Vmp <Vfb< 20% Vmp
Vfb = 15.49% Vmp
The main pool as designed has a 10' vegetated shelf around its perimeter, and has a
cross slope of 10% (10ft hor : 1 ft vert)
Orifice Equation
Q=CdA(2gH)1/2
Cd=0.6
A=∏r2
H=H/3
Pipe Size Area H H/3
(inches) (S.F.) (feet) (feet)
2 0.02 6.2 2.07
V= 38,119 cf
Temporary Pool
Volume
Q= 0.15 cfs
Drawdown= 252421 sec
Drawdown= 2.92 days
Discharge point for pond is an existing concrete drop inlet in the curb of West Front
Street.
There is no proposed fountain.
Project as shown on the attached drawings are full build out of the site. Offsite water is
currently routed around the site.
No know contaminated soils are on this site
SCM slopes are proposed to be 3:1
Erosion control plan approved by Iredell County Planning & Development Erosion
Control Section on 9/17/2018, Project ID STVLE-2018-016. Slope of inlet pipes is
minimized to reduce storm water velocity; pipe inverts were designed to match main
pool elevation. Pond outlet discharges into an existing NCDOT/Municipal storm
drainage system.
Outlet Structure 1 (OS-1) as detailed on sheet C1.1 is designed to bypass excess
flows, including the 100 year storm event.
Outlet Structure 1 (OS-1) as detailed on sheet C1.1 is equipped with an 8” valve for
pond drawdown.
Sediment and erosion occurring during the construction phase of this development will
be contained prior to reaching the pond.
The initial submittal did not include a maintenance easement. Plan sheets C1.0 and
C2.0 have been updated to reflect this information.
The initial submittal did not include an access easement. Plan sheet C1.0 has been
updated to reflect the proposed access easement in favor of NCDEQ-DEMLR. This
easement will be platted after record drawings of the constructed facility are complete.
N/A
Provided in original submittal.
Provided in original submittal.
Design follows wet pond MDC’s pursuant to Rule .1053.
Wet pond designed by person licensed under NCGS 89C-3 (2)
N/A
N/A