20131070 Ver 1_More Info Received_20140624 (17)

Strickland, Bev
From: Devane, Boyd
Sent: Thursday, June 12, 2014 4:23 PM
To: john.vilas @mcgillengineers.com
Cc: Fox, Tim
Subject: Questions about Elk Creek at Banner Elk
I am reviewing the stormwater plan that has been submitted to meet the requirements of the 401 permit for this
project. Although I understand that Banner Elk will also review the stormwater plan, they are not an approved
community for 401 stormwater review so I will be reviewing the plan for the Division of Water Resources. I realize that
the hold put on the project has delayed this work and has diverted me to other projects not on hold. However, I will try
to work as quickly as possible to review and approve the stormwater treatment for the proposed development. The
comments below are from my quick review of the project and I expect to have more as I understand the plans
better. However, I wanted to give you this information so we can start a dialogue that can result in an approvable plan.
1. There are some differences in numbers regarding the volume of the pond and the volume of the forebays. Your
volume of the stormwater to be treated is 11,060 cu ft and is ok, although my figures are 11,301 cu.
ft.. However, there are different numbers in the plan on the size of the pond. I realize that size of treatment
system and size of the pond get confused and are different in different places. However, our Wet Detention
Basin Supplement form specifies that the "Volume, permanent pool" includes the main pond volume and
forebay but excludes the sediment storage. (Click on the red triangles.) The "Volume, permanent pool" space in
your submitted Supplement Form has a figure of 8,412 cu.ft. Did you mean for it to be the 11,003cuft —
500cuft = 10,503 cu ft? It will make the forebay volume be nearer the goal of 20 %.
2. 1 do not see any forebay on the drawing.(9- 13 -13) Have I misread something?
3. On the "Sediment Basin Plan" drawing, the Total Provided Storage number provided is 12,606 cu ft and in
another place the "volume provided in the filter area" is 13,710 cu ft. Why are these numbers different from
the above? The Sediment Basin Plan title is a little confusing since this drawing includes the design of the
sedimentation basin and the converted post- construction stormwater wet detention pond. We are not
interested in the sedimentation pond details and combining the two leads to confusion and delays my review.
4. Related to the above, there is an underdrain and filter fabric on this drawing. Please explain their function.
5. The sediment /detention pond drawing also still refers to the "filter area ". Is there some type of filtration
planned for this wet pond?
6. The Stormwater BMP Manual, the Supplement Sheet and EMC rule 2H .1008 requires that the BMP should be
located in a recorded drainage easement with a recorded access easement to a public ROW. The Supplement
Sheet asked about this and you recorded a "No." Please explain why this is not appropriate for the site.
7. The Stormwater BMP Manual, the Supplement Sheet and EMC rule 2H .1008 requires that a 30' vegetative filter
be installed for the discharge from the pond. Your Supplement Sheet indicates that there will not be
one. Please explain. Having a 90% sediment removal -sized pond will eliminate that requirement.
8. Have the detailed construction drawings been prepared yet? Some of the information needed to make final
approval will probably be provided by them and having them now would facilitate our review.
9. Please discuss how the requirement to design the pond such that no "short- circuiting" will occur will be
met. Chapter 10 of the Stormwater BMP manual has considerable information on pond design.
10. The Stormwater BMP Manual (and EMC rule 2H .1008) requires that the "Vegetated slopes shall be no steeper
than 3:1." Your drawings indicate a 2.5:1 slope although your Supplement Sheet indicates a 3:1 slope.
11. There is little information on the design and materials for the riser. The detailed construction drawing would be
helpful.
12. A drawing specifically showing the drainage area to the pond and the proposed location of impervious areas is
needed to enable review of the plan.

13. The previous O &M form was for a "Dry Extended Detention Basin ". Since this is a wet detention basin, you
cannot rely on the previously- signed form. You can find a list of O &M forms on the bottom left -hand side of the
page where the Stormwater BMP Manual is located at the DEMLR website.
I will not be in the office again until Tuesday.

Strickland, Bev
From: Devane, Boyd
Sent: Tuesday, June 24, 2014 3:53 PM
To: Strickland, Bev
Subject: Please store this email in the #2013 -1070 file
Attachments: Questions about Elk Creek at Banner Elk
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