SW1240401_Response To Comments_20240815

aka
Davis CivilSolutions, PA
August 15,2024
Mr.Jacob Beeker
Stormwater Permitting Engineer
NCDEQ
DEMLR Stormwater Program
1612 Mail Service Center
512 North Salisbury Street
Raleigh,NC 27699-1612
RE: Storm Water Plan for
Mars Hill University
Madison County, North Carolina
Dear Mr. Beeker,
We received your comments for the subject project, via email, dated July 23, 2024.
Information has been revised/updated based on your comments. Revised/additional information is
being provided, sent via FedEx, to the address provided in your letter. Information will also be
uploaded digitally to the web address provided in your comment letter. Revised information
included with this submittal include the following:
• 1 original and 1 copy of the Application
• Original complete Supplement-EZ form,with additional pages
• Original O&M Agreement
• 2 sets of revised plans
• Original revised Calculation Manual
My responses to your comment letter are listed in the same order as your comments:
1. The BUA has been revised to include only that area located within the drainage area of the
proposed SCM. This information is consistent between application and supplemental forms.
Please note that this area is not the total project area and is only being identified for the area
within Drainage Area 1 on all attached documentation.
2. The drainage area to the proposed detention system has been revised. This information can
be found on sheet C-17. Calculations have been revised to include this additional area and
are included with this submittal.
3. The total project area does not equal the drainage area to the proposed detention system.
Information has been revised for clarity, to show drainage area to the proposed detention
system. The 1.88 acre area referenced is the total project area and is not the drainage area to
the proposed system.
a. Based on the total BUA, the project will not be considered low impact and therefore
will achieve "Runoff Treatment". Initial completeness review indicated revisions
necessary to that original submittal, which included revisions to the design and
calculations. The original intent was to provide Runoff Treatment, this information
has been added back to the calculations and can be found within the calculation
Engineering/Planning • Site/Infrastructure
135-A Charlotte Highway • Asheville,North Carolina 28803 • 828.299.9449 PH
[e-mail] EMAIL

Mr. Jacob Beeker
NCDEQ
DEMLR Stormwater Program
August 15, 2024
Page 2
manual for the 1-inch rainfall event.
4. O&M Agreement
a. The O&M Agreement has been revised to include the proposed infiltration trench.
5. Application
a. The BUA areas have been revised such that they are consistent across all documents.
Information outlined on sheet C-17 found in the data block remains unchanged, as
this information is relevant to the total project area, which shows the total net
increase in impervious surface for the project. But, supporting documentation
included with the submittal is specific to the drainage area for the proposed
detention system.
b. The address has been revised.
6. Supplement-EZ Form
a. The cover page has been revised.
b. Drainage Areas Page
i. The Entire Site Column has been revised.
1. The entire site column has been revised. Lines 19-21 have been
omitted.
2. Infiltration trench has been identified.
ii. DA 1 Column — Please note, an additional page has been included with
additional information.
1. This column has been completed.
2. The drainage area for the SCM has been added. As a note,
calculations were revised to include this adjusted area.
3. The appropriate BUA has been added.
4. Information has been added to these cells.
5. Information has been added to this cell.
6. Information has been added to these cells.
c. Infiltration System Page — Please note, an additional page has been included with
additional information.
i. An orifice is included in the weir wall to allow for bypass flows exceeding
initial design storm volumes. A second orifice is located at a higher elevation
on this weir wall to allow for control of larger storm events.
ii. Information has been included on a second page indicating provided
pretreatment.
iii. Soils information has been added to these cells, as provided by the
geotechnical engineer.
iv. The proposed pipe is an arch, but width and height dimensions of the arched
pipes have been included.
7. Plans
a. The drawdown orifice is located within the control structure, box C5. It can be
found on the bottom of the weir wall located within this structure. The initial
drawdown orifice is indicated as a 1/2" orifice, with a secondary orifice, 8", located
at a higher elevation on the weir wall. Calculations were originally revised to omit
this orifice but have been revised a second time to include this orifice. Revised
calculations,with this orifice included, are included with this submittal.
b. The proposed easement has been added to the plan sheet,C-04.

Mr. Jacob Beeker
NCDEQ
DEMLR Stormwater Program
August 15, 2024
Page 3
c. Details outlining the proposed system have been revised slightly to include additional
information or revised information. This information can be found on sheet C-14.
It should be noted that several of the details provided on this sheet are those
developed by the manufacturer, ADS. ADS details include Acceptable Fill Materials,
MC-3500 Technical Specifications, Storrntech General Notes, Underdrain Details, MC-3500
Isolator Row Detail with Inspection Maintenance, and 6" Underdrain Detail. Some
information indicated on these details as well as others on this sheet have been
revised for clarity.
i. As indicated above, several of the details indicated on this sheet are
manufacturer's details. The manufacturer has specified items that are
allowable/acceptable and those which are required, as it relates to the system
as it is installed. Prior to addressing comments provided further in this
section, I would like to provide a brief explanation of the system and how it
is intended to function, such that this could be referred to for subsequent
comments and/or responses:
The proposed system includes a series of arched pipes, chambers, situated between a
diversion box, on the upstream side of the system, and a control box, on the downstream
side of the system. All chambers are sitting on a layer of stone. The lowest portion of stone
is that which is provided to account for infiltration. This layer of stone is wrapped with
geotextile fabric and is 6" thick. The area that this stone occupies is that which is necessary
to provide infiltration based on the infiltration rates determined by the geotechnical
engineer. This layer of stone extends beyond the outside extents of the main chamber
system. Above this initial layer of stone is a second layer of stone,which is 9" thick. This is
the foundation layer for the chamber system. Stone installed in this layer, along with stone
on the sides and tops of all chambers, with the chambers embedded in this stone, are all
wrapped in geotextile fabric. This fabric encapsulates the entire system. Flow is directed to
the diversion structure. This structure has a diversion weir that directs the first flush
through the isolator row. This isolator row addresses water quality, as this row alone is also
sitting on a layer of geotextile fabric. This is the only row that has fabric that the chambers
sit directly onto. Flow enters the isolator row,infiltrates into the foundation stone, and then
into the stone layer below it, the infiltration layer. In larger rain events, flows that are not
infiltrated begin to fill the stone foundation layer above it, and the chambers above that.
There are header pipes that connect each row of chambers together, except for the isolator
row, it only has a single header connection to allow for initial flow to enter from the
upstream side. These header pipes interconnect the system to allow for free flow between
rows of chambers and into stone layers. Orifices in the control structure weir wall limit
discharge of design storm events to predevelopment rates. The smaller orifice in the control
structure holds that runoff in the system to allow for both infiltration and storage of that
runoff. Larger storm events are then controlled by a second orifice located at a higher
elevation on this weir wall. Then, the weir at that top of this wall controls even larger storm
events. This weir wall controls design storm flows, with larger storm events flowing over
this weir wall but are contained within the system.
1. This was found on the manufacturer's detail;it has been removed.
2. This was found on the manufacturer's detail;it has been removed.

Mr. Jacob Beeker
NCDEQ
DEMLR Stormwater Program
August 15, 2024
Page 4
3. Please refer to my explanation above for locations of geotextile
fabric. Details on the plan sheets indicate foundation stone depth,
9", infiltration layer stone depth, 6", side stone width, 12", and stone
cover, 12".
4. ADS detail Acceptable Fill Material outline fill material (stone) which is
acceptable for use as foundation stone, and stone installed along the
sides and above the chambers. #57 washed stone is specified for the
infiltration layer, below the system, as indicated on the section detail,
Section A-A, on sheet C-14.
5. Please refer to my explanation above for additional clarification.
Chambers sit directly on a 9" thick foundation stone layer, with a 6"
thick infiltration layer below that, extending beyond the extents of
the foundation layer. Elevation information has been added to the
section detail,Section A-A,on sheet C-14.
6. Please refer to my explanation above for additional clarification. The
6" thick stone infiltration layer is completely wrapped in fabric. The
entire system of stone, including the foundation layer, and chamber
system is wrapped in fabric,which sit directly on the infiltration layer.
ii. Elevations have been added to the detail,Section A-A,on sheet C-14.
iii. A note has been added regarding the SHWT, to Section A-a on sheet C-14,
as well as to notes found in the lower left corner of sheet C-04.
iv. The system has been revised slightly to include header pipes on the
downstream side of the system, connecting all rows except for the isolator
row. The outlet structure detail shows this header, the Site Detail has been
revised to include this additional information.
8. No comment
9. Revised documents
a. PDF files will be uploaded using the link provided.
b. Hardcopies of the same, including originals of signed documents are being sent via
FedEx to your attention.
We appreciate your review of the attached and trust the information provided is satisfactory
for review and ultimate approval. Should you have any questions or require additional information,
please feel free to call. We appreciate your assistance.
Sincerely,
DAVIS CIVILSOLUTIONS,P.A.
NICHOLAS M. BOWMAN
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