SW3170305_Response to Comments_20170510

Larkin MF Development
Response to Comments Dated April 04, 2017
Date of Response: May 05, 2017
Stormwater Permitting Program (Robert Patterson)
1. All SCMS must comply with all MDC in 15A NCAC 02H.1000 and the latest SCM Design Manual.
SCMS checked against new MDC design standards in the SCM Design Manual.
2. The person signing the application and O&M agreement must be an officer of the corporation
listed on the NC Sec. of State's website. Or provide a signed letter from one of the officers
listed giving Michael Foss signature authority.
We are still currently waiting on receiving the newly signed O&M agreement and authorization
letter from the owners and will provide those once received.
3. The rules require the runoff from all BUA to be treated. As currently proposed, approximately
20% of the roof areas is not being treated in a SCM. Evaluate adding piping and/or swales to
capture the rear roof areas on lots 2, 3, 14-17, 19, 20, and 25-29.
Grading plan revised with rear yard ditches to route rear roof runoff to be treated in a SCM.
4. Where does the roadside ditch along Amity Hill Road, where the wet pond discharges, drain
to? Does it drain to Third Creek, or Duck Creek to the south?
The roadside ditch along Amity Hill Road drains to the south into Duck Creek prior to draining
into Third Creek. This has been updated on the Stormwater Management Permit Application.
5. Provide signed and notarized O&M Agreements for the SCMS (General MDC 11). The new
O&M EZ form is available on our website.
The new O&M EZ form has been filled out, signed, and provided with this submittal package.
6. Please consider using the discrete SCS method of Simple Method for calculating the WQV.
Using composite CN will yield an artificially lower volume. General MDC 1 requires a sufficient
sized SCM. See also Part B of the SCM Manual.
The Simple Method was applied in calculating the WQV.
7. The DA and BUA is not consistently shown between SWU-101, Sht. Post DA, and the
supplement forms. Revise so all are consistent.
The DA and BUA have been checked and adjusted where applicable to be consistent on the
SWU-101, supplement forms and Sht. Post DA.

8. Note there are new supplement forms using Supplement EZ found on our website.
The new supplemental forms for wet ponds and sand filters have been completed and
submitted with this package.
9. All 3 SCMS:
a. The CN is not consistent between Sht. Post DA and the calcs.
The CN values used for the calculations have been updated on the Sht. Post DA.
b. Provide supporting calcs. for the WQV based on the 1" design rainfall depth. (General
MDC 1)
Supporting calculations for WQV provided with this revised submittal.
c. Extend the SCM easements to the nearest public RoW. (General MDC 8)
The SCM easement has been extended to the nearest public RoW
10. Wet Pond #100:
a. Provide supporting calcs. for the surface area using SA/DA tables or HRT method in
MDC 1.
Supporting calculations provided for calculating surface area using SA/DA
method.
b. Provide supporting calcs. for the main pool depth using option 1 or 2 in MDC3.
Main pool depth provided in calculation design book for permanent pool.
c. Provide supporting calcs. for the forebay size (MDC5).
Supporting calculations for forebay size provided with this revised submittal.
d. Provide supporting calcs. demonstrating the WQV draws down in 2-5 days (MDC7).
Supporting calculations provided with this submittal package showing that the
WQV draws down in 2-5 days in accordance with MDC7.
e. Add contours to Sht. BMP -2 to show the actual excavated depth for the sediment
storage. Also, add the elevation to the profile of the bottom of the sediment storage.
Contours and contour labels have been added to sheet BMP -2 to show the
actual excavated depth and bottom of the sediment storage.
11. Both Sand Filters:

a. Provide a soils report for the SWHT elevation for each sand filter. This must be based
on an in-situ soils evaluation. (MDC 1)
A soils report of the in-situ soils to determine the SHWT elevation was produced
by Summit Engineering and the report has been included with this submittal.
b. Provide a mechanism to evenly distribute flow over the sand surface. (MDC 5)
Both sand filter ponds use a rip -rap apron along the forbay to evenly distribute
the flow over the sand surface.
c. Specify on Shts. BMP -4 and BMP -5 that ASTM C33 or equivalent sand must be used.
(MDC 6)
A note has been added to sheets BMP -4 and BMP -5 stating that ASTM C33 or
equivalent sand is to be used.
d. Revise the stage storage tables to show the cumulative volume at the design WQV
elevation.
The design storage table has been updated to show the cumulative volume at
the design WQV elevation for each sand filter pond.
e. Revise the stage storage tables to breakdown the areas, stage, and volumes for each
sediment chambers and the sand chambers.
Additional pages have been added to show the storage breakdown for each
sediment and sand chamber.
12. Sand Filter #200:
a. Open sand filters require 2' of separation from SHWT elevation to the bottom of the
sand layer (MDC 1). The supplement form states there is negative separation.
Based on the soils report of the in-situ soils there is greater than a 2 foot
separation between the bottom of the sand layer and the SHWT. This has been
updated on the new Supplemental forms.
b. The elevations are not consistent between the supplement forms and the plans.
The elevations between the supplemental forms and the plans have been
revised where applicable to be consistent.