SW3230608_Response To Comments_20231014

DEMLR Comments with Responses
10/3/2023
1. Please clarify whether the drainage area to the SCM is 11.8 ac or 11.52 ac as both values are
shown in the submittal materials (for example, the application lists 11.8 ac while the drainage
area plan(C-7) shows 11.52 ac). Please revise as needed for correctness and consistency.
NOTE: Since it is unclear what the actual drainage area to the SCM is, some aspects of the
design could not be fully reviewed for compliance with the rules at this time.
Response: Drainage area to SCM is 11.52 acres and has been revised throughout plans and
application.
2. Per the provided drainage area map, the point of discharge from the off-site bypass DA 2 pipe
system is located within the drainage area to the SCM(and would therefore drain to the SCM).
Please revise as needed.
Response: Drainage area map has been revised. DA2 will not drain to SCM. Additional note
as been added to Storm Drainage plan directing contractor to direct flow off site.
3. Please provide the sizing/design calculations for the proposed sand filter. From the provided
submittal items, it is unclear where the minimum required treatment volume, design volume,
and volume that can be stored within the sediment chamber and sand chamber came from. It is
recommended to split the stage storage table into a sand and sediment chamber part so the
volumes provided in each can be verified. It is also recommended to include the cross-sectional
area of the sand& sediment chambers at the invert of the lowest bypass elevation(768.45') as
this determines the design volume. Please revise as needed. NOTE: Since these calculations
were not provided, some aspects of the design could not be fully reviewed for compliance with
the rules at this time.
Response:Additional information section has been provided including Split storage table
with area of sand&sediment at invert of lowest bypass. Information is included in the
Stormwater Report(Water Quality Storage Table). Supplemental form has been updated.
4. Please provide the Seasonal High Water Table(SHWT) elevation for the sand filter(This
information is required per Sand Filter MDC 1). The provided soils report indicates the depth
from the existing ground surface elevation to groundwater(which is not the same as the
SHWT). If the boring will only include the depth from the existing ground surface, please
ensure that the elevation of the existing ground surface is also provided so the elevation of the
SHWT can be calculated. Please revise as needed.
Response:Additional informational section (Seasonal High Water Table Information) has
been added to the Stormwater Calculations including cross section of the test hole location at
the SCM and an explanation for calculations of the existing grade and SHWT.
Note that the soil information within the report was inconclusive as to SHWT and it is
assumed the depth of the water seepage (140"or 762.8) to be the SHWT. Also note that
the SHWT elevation on the original Supplement form has been revised as per the calculation.

5. Please indicate on the deed restriction document that Lot 5,the SCM lot, is not allocated
3,500 sf of BUA.
Response: Deed restriction form has been revised. Note that allocated BUA is 3,600 SF.
6. Please correct the following issues with the Application:
a. Section II, 5 —This project is located within 5 miles of Mid-Carolina Regional Airport.
Projects that are located within 5 miles of an airport are strongly recommended to use
SCMs that do not promote standing water in accordance with G.S. 143-214.7(c3)
https://www.ncleg.gov/EnactedLegislation/Statutes/HTML/BySection/Chapter_143/GS_143-
214.7.html .Alternative SCMs that can be used within the 5 mile radius of a public airport are
outlined in Part E-4 of the Manual https://deq.nc.gov/media/9977/download.
Response: Form has been revised. Sand filters are allowable alternative.
b. Section III, 1.c.—Please indicate that the Applicant is the Property Owner.
Response: Form has been revised.
c. Section III, 2 & Section IX—Since the Applicant is also the Property Owner, this
information should not be provided. With your permission, I can cross out the original,
signed Section IX. Revised hard& electronic copies of the Application should reflect this
change. Please revise as needed.
Response: Form has been revised.
d. Section IV, 10—Please list the BUA allocated to the individual lots (111,600 sf)under"On-
site Buildings/Lots"instead of"Future". Please also see earlier comment with regard to the
drainage area value and revise as needed.
Response: Form has been revised.
e. Section IV, 11 —This item is only required if there are off-site areas that are draining to the
proposed SCM.
Response: Form has been revised.
7. Please correct the following issues with the Supplement-EZ Form:
a. Cover Page:
i. Line 7—Please include this item. It is noted that there are no surface waters located on-
site, however we require this item to be completed.
Response: Revised.
b. Drainage Area Page:
i. Line 2—Please enter 1 drainage area since 1 SCM is proposed for this project.
ii. Drainage Area Table—Please provide and complete this table(adding the drainage area to
Line 2 and clicking on"load forms" should create the table). The entire site column should be
an accounting of the entire project area(whether or not the areas drain to the SCM) and the
drainage area column should be an accounting of all of the areas that drain to the SCM
(whether or not they are located within the project area). The "drainage area" for the entire
site column refers to the project area(Section IV, 7 of the Application) and the drainage area
column should correspond to the information shown in Section IV, 10.

Response: Revised.
c. Sand Filter Page:
i. Line 2—Please clarify where this value came from. This value is determined by the Simple
Method or Discrete NRCS Method and is based on the area draining to the SCM.
Response:Additional section detailing the Simple Method has been added to Stormwater
Report.
ii. Line 18—Please revise as needed(see earlier comment).
Response: Revised as per above.
iii. Lines 23 & 30— See earlier comment with regard to the stage-storage table so these values
can be verified. The sum of these values is equal to the design volume of the sand filter and is
equal to the volume that can be stored between the"bottom" of the sand filter(@ elevation
767.2' per the plans) and the invert of the lowest bypass device (weir @ elevation 768.45').
Per Sand Filter MDC 2, the volumes provided in each chamber shall be equivalent. If the
sediment chamber is being oversized, half of the minimum required treatment volume should
be provided in both the sediment and sand chamber(see guidance in the Manual for more
information).
Response:Additional section "Water Quality Storage Table"has been added to the
Stormwater Report. The SCM meets requirements for minimum half of required treatment
storage being contained in sand chamber.
iv. Line 25 —Please provide the elevation of the bottom of the sediment chamber("Yes" is not an
elevation).
Response: Revised. Note that the spreadsheet has an error and only allows for yes/no
answers.
v. Lines 26 & 32—These values correspond to the cross-sectional area of the sediment and sand
chamber at the"bottom" elevation(767.2' per the plans). These values should correspond to
the information shown in the stage-storage table. Please revise as needed.
Response: Revised.
vi. Line 33 —The physical depth of the sand chamber is the distance from the excavated bottom
of the sand chamber(below the underdrain)to the invert of the bypass device.
Response: Revised to 43 inches. Note that the original comment referenced Line 34. It has
been revised to say 33.
vii.Line 36—Please indicate if the bypass device is an orifice or a weir.
Response: Revised. Bypass is a weir.
viii. Please also update any information on this page that changes while addressing the other
comments.
Response: Revised.

8. While not required, it is strongly recommended to select a more appropriate SCM for this
drainage area. Sand filters with a drainage area of over 5 acres and sand filters with a high
pervious percentage of their drainage area are prone to maintenance issues which can become
costly over the life of the SCM. Please consider a different SCM for this site or reconfiguring
the SCM design.
Response: Noted. No revisions made.