SW7110601_COMPLIANCE_20110607

STORMWATER DIVISION CODING SHEET
POST -CONSTRUCTION PERMITS
PERMIT NO.
SW 7c�
DOC TYPE
❑ CURRENT PERMIT
❑ APPROVED PLANS
HISTORICAL FILE
COMPLIANCE EVALUATION INSPECTION
DOC DATE
YYYYM M DD

STORMWATER SUBMITTAL REQUIREMENTS SW 7K�C,0
WET DETENTION POND
I. Objective
A. Collect all runoff from all BUA (proposed and/or existing and/or offsite) as the case may be,
by any means including piping or swales, and direct it to the pond.
B. Check the proposed pond design to make sure it meets or exceeds the minimum design
criteria for surface area, volume and drawdown.
Il. What makes up a complete wet detention pond application package?
A. Two sets of sealed, signed & dated layout & grading plans with appropriate details.
(Additional sets of plans may be requested for projects in certain counties)
B. Completed application with supplement(s), SWU-101, SW401-Wet Pond, and inspection and
maintenance agreements.
C. Deed restriction document, if applicable (for subdivisions & projects with out parcels)
D. Sealed, signed & dated calculations.
E. Estimated seasonal high water table elevation at all pond locations.
F. Chlorides test results must be provided if the project is within Yz mile of SR waters (Phase 11).
(This is only required to test out of SR water treatment requirements)
III. BIMS entry (for DWQ use only)
Enter & track application acknowledged date, review date, add info requested/received dates, permit
issue dates, and drainage area info. Best done after the add info letter is written and before sending
permit up for signature.
IV. Shell documents (for DWQ use only)
Permit shells: s:\wqs\stormwater\shells\highcom pond
s:\wqs\stormwater\shells\highsubpond
s:\wqs\stormwater\sheils\HDhybrid
Spreadsheet: s:\wqs\stormwater\excel spreadsheets\pond
VI. Review Procedure
A. APPLICATION
1. ✓An original signature is required. Photocopied signatures cannot be accepted.
2. � completed wet detention pond supplement and a signed, dated and notarized wet
detention pond Inspection and Maintenance Agreement with an original signature.
3.' The numbers on the supplement match up to the numbers used in the calculations and
shown on the plan details.
4. Built -upon areas are reported in square feet in Section 111.6.
5. Receiving stream name and classification. This is important because in the non -Phase
11 counties, a wet pond cannot be used on a project that is within'/2 mile of and draining
�/to,SA waters. For Phase 11, a wet pond is allowed within Yz mile of SA waters.
6. Section 111.6 is filled in -cannot be left blank. One column must be filled in for each
proposed wet pond.
7.�/ If the applicant is a corporation, partnership or LLC, look it up on the Secretary of State
Corporations Database. Make sure corporation is spelled correctly (capitalization and
punctuation matter) and that the person signing the application is at least a vice-
president in the corporation, a General Partner in the partnership, a member in a
member -managed LLC, or the manager of a manager -managed LLC. Need
documentation to support if the Articles of Incorporation do not list the members or
managers of the LLC. If an agent signs, then a letter of authorization is needed from the
president, vice president, general partner, member or manager.
81KFor subdivided projects, a signed and notarized deed restriction statement must be
1 SSrr provided.

Wet Detention Pond, cont
B. CALCULATIONS
1. The orifice is sized based on drawing down the calculated minimum volume in 2-5
days. The average head to use in the orifice equation is approximately one-third of
the distance between the permanent pool elevation (PPE) and the elevation of the
next available outlet above the permanent pool. The elevation of the next available
outlet must be either the elevation where the minimum volume is provided, or it can
be higher. The temporary pool elevation (TPE) to report on the supplement will be
the elevation of the next available outlet above the PPE. The temporary pool volume
(TPV) to report on the supplement is the volume between the specified PPE and the
TPE.
2. For Phase II projects that are within '/z mile of and draining to SR waters, the
difference in runoff from the predevelopment and post -development conditions for
the 1 year 24 hour storm must be controlled and treated.
3. For Phase II projects, the discharge rate leaving the pond can be no more than the
pre -development discharge rate for the 1 year 24 hour storm.
4. For Phase II projects draining to SA water, no discharge to surface waters may occur
from wet ponds. The discharge leaving the orifice must be effectively infiltrated prior to
reaching surface waters.
5. The average pond depth is the permanent pool volume divided by the permanent pool
surface area. The result must be between 3 ft. and 7.5 ft. Parts of the pond can be
deeper than 7.5 ft., but in no case can any part of the pond be less than 3 ft deep.
6. If the 85% TSS chart is used a 30' vegetated filter must be provided at the outlet of the
pond. If the 90% TSS chart is used, no filter is required.
7. Use the correct SA/DA TSS chart from the BMP Manual noting that there are different
charts for different areas of the State.
8. Required surface area at permanent pool.
9. Provided surface area at permanent pool (Based on pond dimensions)
10. Required volume calculation based on 1.5" storm for Phase II projects' and 1" storm for
all others projects. 'unless the project is Phase II and within '/z mile of and draining to
SR waters then the volume calculation must be based on difference between the pre
and post development conditions for the 1-yr 24-hr storm.
11. Table of elevations, areas, incremental volumes and accumulated volumes for overall
pond and for forebay, to verify volumes provided.
12. Forebay designed to hold 20% of the permanent pool volume. (Range of 18%-22%
OK.)
13. Non -erosive flow for 10 yr. storm in the vegetated filter, if using 85% TSS.
14. The seasonal high water table must be at or below the proposed permanent pool
elevation to assure that the necessary volume will be available above the permanent
pool.
15. Rounding numbers off during the calculation process can result iri deficiencies. Do not
round the numbers until you get to the final result.
16. An additional one foot must be excavated below the bottom elevation of.the pond. The 1
foot sediment accumulation depth is not included in the average depth calculation.

-i. Wet Detention Pond, cont.
C. PLANS- Due to storage space constraints, plan sheets should be kept to a minimum. For
small commercial single wet pond projects, the plan set could consist of only 2 or 3 sheets,
layout, grading and details. For larger projects, show as much information as possible on as
few sheets as possible, without cluttering them up.
1. ✓ Development/Project Name
2. Engineer name and firm.
3. '/LLegend
4.1//North Arrow
5. Location Map with nearest intersection of two major roads shown. Major road is any 1,
✓2, or 3 digit NC, US or interstate highway.
6. Scale- standard engineering scale, no off-the-wall stuff.
7.. /Date
8. V Revision number and date, if applicable.
9.�Original contours, proposed contours, spot elevations, finished floor elevations, pipe
Xnverts, swale inverts, etc.
1 OY Existing drainage (piping, swales, ditches, ponds, etc.), including off -site. Include a map
delineating the offsite drainage areas.
11!�/,Property/Project boundary lines, bearing & distances.
12 ,Property/Project
High Water Line or Normal High Water Line, if applicable.
13.y The permanent pool elevation must be above the SHWT and above the lowest
elevation of adjacent wetlands. Evaluate the need for a liner and/or berm/slurry wall to
prevent dewatering the wetland.
14V /Drainage easement widths, pipe sizes and swale inverts are provided.
15.✓/ Wetlands delineated, or a note on the plans that none exist. Get a copy of the wetlands
delineation map signed by the Corps of Engineers, or have the applicant include a copy
of the unsigned delineation map submitted to the Corps. Wet ponds may not be located
n wetlands unless a permit to fill those wetlands has been obtained.
16 Details for the roads, parking, cul-de-sacs, including sidewalk width, radii, dimensions &
slopes.
iqkApartment / Condo development- Provide a typical building footprint with dimensions
/and note all concrete and wood deck areas.
18. The drainage area for each wet pond is clearly delineated and numbered to match up to
the calculations and supplement. Drainage area delineation is best done as a separate
plan sheet.
19✓A pond section detail to include the forebay, a 10 foot wide vegetated shelf, pertinent
elevations for the bottom, permanent pool, temporary pool, and SHWT, 3:1 slopes
above the permanent pool, and the weir elevation between the main pond and the
{forebay.
20v The 10 vegetated shelf extends 6" below and 6" above the permanent pool elevation.
21 N An outlet structure detail showing a trash rack with :56" square openings, the necessary
orifice invert elevation (i.e., the permanent pool), orifice size and temporary pool
elevation.
22../ Dimensions for each line and arc formed by the permanent pool contour.
2340 Where the 85% TSS chart was used, a 30 ft. vegetated filter strip is required to be
shown on the plans & detailed (elevations, inverts, slopes, and flow spreader
mechanism). Please note that the filter strip is not a ditch.
24.✓A forebay is provided for each inlet and located so as to prevent short-circuiting.
25✓ The pond must have a minimum 1.5:1 length to width ratio and a minimum 3:1 flow path
length. Artificial "baffles" of timber, vinyl, or earth can be used to create a longer flow
path. The top elevation of the baffle should be set at the temporary pool elevation or
higher.
26. A Vegetation plan is specified for the pond, including slopes. Wetlands species are
listed for planting on the 10:1 shelf. Weeping Love Grass is not suitable as a permanent
vegetated cover for pond slopes.
27.✓All roof drainage must be directed to the pond. Show the roof drain collection lines on
the plan. This is necessary for projects where the buildings back up the property lines
where roof drainage may leave the site prior to going through the pond.